Wireless communication device and wireless communication method

ABSTRACT

According to one embodiment, a wireless communication device includes: a receiver configured to receive a first frame notifying a start of resource unit-based OFDMA (Orthogonal Frequency Division Multiple Access) communication via a first channel; and controlling circuitry configured to control, when the first frame is received, the receiver to perform standby operation at least in a first resource unit in a second channel different from the first channel, wherein the first resource unit includes one or more subcarriers among a plurality of subcarriers disposed in the second channel.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of International Application No.PCT/JP2016/058367, filed on Mar. 16, 2016, the entire contents of whichis hereby incorporated by reference.

FIELD

Embodiments of the present invention relate to a wireless communicationdevice and a wireless communication method.

BACKGROUND

Multi-user multi-channel (MU-MC) communication in which a plurality ofterminals simultaneously use a plurality of channels has been attractingattention. The MU-MC communication is called channel-based OFDMA(Orthogonal Frequency Division Multiple Access) communication as well.In the MU-MC communication, for example, a method of simultaneouslytransmitting data from a terminal (a base station, etc.) on atransmission side to a plurality of terminals on a reception side usinga plurality of channels other than a primary channel has been examined.When the terminals on the reception side perform the MU-MC communicationwith the base station, if standby operation is performed in a largenumber of channels, power consumption increases. Therefore, it isdesirable to suppress the standby operation in channels not used in theMU-MC communication by the own terminals. If time in which the standbyoperation is performed in the channels is long, power consumptionincreases. Therefore, it is desirable to reduce the time in which thestandby operation is performed in the channels as much as possible.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a configuration diagram of a wireless communication systemincluding a base station and terminals according to an embodiment;

FIG. 2 is a block diagram showing a wireless communication devicemounted on the terminal according to the embodiment;

FIG. 3 is a block diagram showing a wireless communication devicemounted on the base station according to the embodiment;

FIG. 4 is a diagram showing a basic format example of a frame in theembodiment;

FIG. 5 shows diagrams showing a format example of information elements;

FIG. 6 shows diagrams showing another format example of the frame and aformat example of an HT Control field in the embodiment;

FIG. 7 shows a schematic configuration example of a physical header;

FIG. 8 is a diagram showing an example of an operation sequence of abase station and a plurality of terminals;

FIG. 9 is a diagram showing another example of the operation sequence ofthe base station and the plurality of terminals;

FIG. 10 is a diagram showing still another example of the operationsequence of the base station and the plurality of terminals;

FIG. 11 is a diagram showing still another example of the operationsequence of the base station and the plurality of terminals;

FIG. 12 shows diagrams showing filter setting examples of the basestation and the terminal;

FIG. 13 shows diagrams showing other filter setting examples of the basestation and the terminal;

FIG. 14 shows diagrams showing still other filter setting examples ofthe base station and the terminal;

FIG. 15 shows diagrams showing still other filter setting examples ofthe base station and the terminal;

FIG. 16 shows diagrams showing still other filter setting examples ofthe base station and the terminal;

FIG. 17 is a flowchart of an example of the operation of the terminalaccording to the embodiment;

FIG. 18 is a flowchart of an example of the operation of the basestation according to the embodiment;

FIG. 19 is an explanatory diagram of a resource unit; and

FIG. 20 is an explanatory diagram of channel arrangement.

FIG. 21 is a diagram showing an exemplary overall configuration of aterminal or a base station;

FIG. 22 is a diagram showing an exemplary hardware configuration of awireless communication device equipped at a base station or a terminalaccording to an embodiment;

FIG. 23 is a perspective view of a terminal according to an embodiment;

FIG. 24 is a diagram showing a memory card according to an embodiment;and

FIG. 25 is a diagram showing an example of frame exchange during acontention period.

DETAILED DESCRIPTION

According to one embodiment, a wireless communication device includes: areceiver configured to receive a first frame notifying a start ofresource unit-based OFDMA (Orthogonal Frequency Division MultipleAccess) communication via a first channel; and controlling circuitryconfigured to control, when the first frame is received, the receiver toperform standby operation at least in a first resource unit in a secondchannel different from the first channel, wherein the first resourceunit includes one or more subcarriers among a plurality of subcarriersdisposed in the second channel.

Hereinafter, embodiments of the present invention will be described withreference to the drawings. The entire contents of IEEE Std 802.11™-2012and IEEE Std 802.11ac™-2013, known as the wireless LAN specification areherein incorporated by reference in the present specification.

First Embodiment

FIG. 1 is a configuration diagram of a wireless communication systemincluding a wireless communication base station and wirelesscommunication terminals according to a first embodiment. The wirelesscommunication system communicates according to the IEEE802.11 standard.However, the IEEE802.11 standard is an example. The wirelesscommunication system may communicate according to other wirelesscommunication scheme. In the following explanation, the wirelesscommunication base station is referred to as base station and thewireless communication terminal is referred to as terminal. The basestation is a form of the terminal. The base station is mainly differentfrom a non-base station terminal in that the base station has a relayfunction.

Terminals (STAB: STAtions) 201, 202, 203, and 204 are connected to abase station (AP: Access Point) 101 to form one wireless communicationsystem or a wireless communication group. The connection means a statein which a wireless link is established. The terminals complete exchangeof parameters necessary for communication through an association processwith the base station, whereby the wireless link is established. In thisstate, the base station and the terminals grasp capabilities of theterminals and the base station each other. In FIG. 1, four terminals areshown. However, five or more terminals may be present or three or lessterminals may be present.

The base station 101 can simultaneously perform reception ortransmission with a plurality of terminals using a plurality of wirelesschannels (hereinafter, channels) within a predetermined frequency band.The base station allocates one or a plurality of channels to theterminals and simultaneously performs reception or transmission with theterminals. Such a communication scheme is called channel-based OFDMA(Orthogonal Frequency Division Multiple Access) scheme or multi-usermulti-channel (MU-MC) communication scheme. A terminal corresponding tothe channel-based OFDMA or the MU-MC communication scheme is sometimescalled MU-MC compliant terminal (or IEEE802.11ax adapted terminal). Alegacy terminal not adapted to the MU-MC may be present in the wirelesscommunication system. The legacy terminal performs communicationaccording to a standard such as IEEE802.11b/g/n/ac.

In this embodiment, it is assumed that, as the plurality of channelspresent within the predetermined frequency band, there are eightchannels of a channel 1 to a channel 8 in order from a low frequencyside. The numerals 1 to 8 of the channels 1 to 8 represent channelnumbers. For example, the channel 1 means a channel having the channelnumber 1. Note that, in the figure, the base station and the terminalsare drawn as if each of the base station and the terminals includes oneantenna. However, actually, each of the base station and the terminalsmay include one or a plurality of antennas. Note that, when channelshaving assumed unit channel width (e.g., 20 MHz width) are disposed notto overlap one another, the channel numbers are numbers defining thesechannels for convenience.

In this embodiment, it is assumed that the channel numbers are higher ascenter frequencies are higher. However, this is an example. The order ofthe center frequencies and the order of the channel numbers do not needto coincide with each other. In this embodiment, the channel-based OFDMAscheme (the MU-MC communication) is used in this way. However, aresource unit-based OFDMA scheme for respectively allocating resourceunits, which has one or a continuous plurality of subcarriers as oneunit, to terminals in a continuous frequency domain and simultaneouslycommunicating may be used.

For example, as shown in FIG. 19, a plurality of channels are disposedin a frequency domain. The width (e.g., 20 MHz) of each one channel is acontinuous frequency domain. In one channel, a plurality of subcarrierscontinuous in terms of frequency are orthogonal to one another. Aresource unit (which may be referred to as sub-channel, resource block,or the like as well), which has one or a continuous plurality ofsubcarriers as one unit, is defined. One or a plurality of resourceunits are allocated to the terminals. A scheme for allocating theresource unit to the terminals and simultaneously communicating isreferred to as resource unit-based OFDMA scheme. In FIG. 19, resourceunits (RU#1, RU#2, . . . , RU#K) secured in a continuous frequencydomain in one channel (described as channel M) are shown. One or moresubcarriers (guard subcarriers) may be disposed among the resourceunits. However, the guard subcarriers are not essential. The number ofguard subcarriers is not limited to two and may be optional if thenumber is one or more.

The resource units may be allocated to the terminals in units of theresource units using one or a plurality of the channels 1 to 8 in thisembodiment. In this case, the number of subcarriers per one resourceunit is set the same in the channels. However, the number of subcarriersper one resource unit may be difference among the channels. The numbersof subcarriers in the resource units belonging to the same channel areset the same. However, the numbers of subcarriers may be different inthe resource units. One or a plurality of resource units in one channelmay be allocated to the terminals. A plurality of resource unitsbelonging to a plurality of channels may be allocated to the terminals.The number of subcarriers in the channel may change according to thenumber of channels used in the resource unit-based OFDMA communication.For example, when one channel is used in the resource unit-based OFDMAcommunication, the number of subcarriers in the channel may be set to X.When two channels are used, the number of subcarriers per one channelmay be set to X/2. In this case, when the number of subcarriersdecreases, the bandwidth of the subcarriers increases according to thedecrease in the number of subcarriers. Conversely, when the number ofsubcarriers increases, the bandwidth of the subcarriers decreasesaccording to the increase in the number of subcarriers. Note that, whenthe resource units are decided to be all subcarriers in one channel, theoperation of the resource unit-based OFDMA is considered to besubstantially the same as the operation of the channel-based OFDMA.

The following explanation is based on the channel-based OFDMA scheme forallocating the channels to the terminals in units of channels. However,when the resource unit-based OFDMA scheme for allocating the resourceunits to the terminals in units of resource units is used, in thefollowing explanation, the resource unit-based OFDMA scheme can beimplemented by, for example, reading the channels as the resource unitsand reading the channel-based OFDMA (MU-MC) as the resource unit-basedOFDMA. Note that, in a normal operation period in which communication ofthe OFDMA system is not performed irrespective of the resource unit baseor the channel base, communication may be performed using, as a basicchannel, a primary channel commonly recognized in a system. In theprimary channel, monitoring and transmission and reception may beperformed even while communication of the resource unit-based OFDMAscheme is performed. Note that, as directions of communication intransmitting data in the channel-based or the resource unit-based OFDMA,there are downlink from the base station to the terminals and uplinkfrom the terminals to the base station. In this embodiment, the downlinkis mainly assumed. However, in the case of the uplink, communication canbe implemented as in this embodiment.

In the base station and the terminals shown in FIG. 1, wirelesscommunication devices for performing communication with each other aremounted. The wireless communication devices mounted on the terminalscommunicate with the wireless communication device mounted on the basestation. The wireless communication device mounted on the base stationcommunicate with the wireless communication devices mounted on theterminals.

FIG. 2 is a block diagram of the wireless communication devices mountedon the terminals.

The wireless communication device of the terminal includes one or aplurality of antennas, a PHY processing and wireless unit 20, a MACprocessor 30, and an upper-layer processor 40. The MAC processor 30includes a transmitter 31, a receiver 31, a first controller 33, asecond controller 34, and a timer 35. A controller is divided into thefirst controller 33 and the second controller 34. However, the firstcontroller 33 and the second controller 34 may be collected as onecontroller. The MAC processor 30 or a set of the MAC processor 30 andthe PHY processing and wireless unit 20 corresponds to an integratedcircuit for wireless communication in this embodiment. The entire or apart of processing of digital regions of the units or processing of theintegrated circuit for wireless communication may be performed bysoftware (a program) operating in a processor such as a CPU, may beperformed by hardware, or may be performed by both of the software andthe hardware. The terminal may include a processor that performs theentire or a part of the processing of the units.

The PHY processing and wireless unit 20 includes one or a plurality oftransmission and reception processors. When X represents an integerequal to or larger than 1, the PHY processing and wireless unit 20includes first to X-th transmission and reception processors. Antennasare respectively connected to the transmission and reception processors.One transmission and reception processor may be disposed for each onechannel. When a plurality of channels are collectively processed, onetransmission and reception processor may be disposed for the pluralityof channels. When one transmission and reception processor is disposedfor each one channel, if the wireless communication device is adaptableup to eight channels, the PHY processing and wireless unit 20 includeseight transmission and reception processors in order to performprocessing for each one channel. In an example shown in the figure, theantenna is connected to each of the transmission and receptionprocessors. However, one antenna may be connected to the plurality oftransmission and reception processors in common. In this case, theplurality of transmission and reception processors, to which one antennais connected in common, only have to extract signals of channelsrespectively allocated to the own processors. The transmission andreception processors may extract signals for all channel bands with ananalog filter that covers all or a plurality of channels and extractsignals of channels of the own processors with digital filters or mayextract signals with analog filters corresponding to only channel bandsof the own processors. An operation band of the analog filter may bevariable according to an instruction of the second controller 34. Theanalog filter may have an operating band that is variable according todesignation by the controller 34, or may be capable of supporting onlysignals in a preliminarily fixed band. Concerning transmission, thetransmission and reception processors may respectively correspond toseparate channels or may correspond to all or a plurality of channels.Information concerning channels processed by the transmission andreception processors is managed by the second controller 34. The secondcontroller 34 allocates channels to be processed to the transmission andreception processors and indicates the allocated channels to thetransmission and reception processors. The transmission and receptionprocessors process the channels indicated by the second controller 34.

The first controller 33 manages an access to channels and controlstransmission of a frame at desired timing. The first controller 33 mayuse the timer 35 in order to perform the frame transmission at thedesired timing. The first controller 33 sets a time period until a timeof the desired timing in the timer 35. When the timer 35 times out, thefirst controller 33 executes frame transmission. The transmitter 31performs generation and transmission of a frame. When transmission of aframe is instructed from the first controller 33, the transmitter 31generates the instructed frame and outputs the generated frame to thePHY processing and wireless unit 20. The PHY processing and wirelessunit 20 inputs the frame input from the transmitter 31 to thetransmission and reception processor of a channel corresponding to theframe. The transmission and reception processors perform processing of adesired physical layer on the frame input from the transmitter 31,perform D/A conversion, frequency conversion, and the like on the frame,and transmit a signal from the antennas to the space as a radio wave.Note that the frame in this embodiment is not limited to what is calledframe in, for example, the IEEE802.11 standard and may be what is calledpacket.

The first controller 33 and the second controller 34 may access astorage device and read out information to be transmitted to the basestation or may store information received from the base station in thestorage device. The storage device may be a buffer (an internal memory)included in the first controller 33 or the second controller 34 or bothof the controllers or may be a buffer (an external memory) provided onthe outside of the first controller 33 or the second controller 34. Thestorage device may be a volatile memory such as a DRAM or may be anonvolatile memory such as a NAND or a MRAM. Besides the memories, thestorage device may be an SSD, a hard disk, or the like.

The transmission and reception processors of the PHY processing andwireless unit 20 convert signals received via the antennas from wirelessfrequencies into basebands and extract signals of channels correspondingto the basebands from baseband signals. The transmission and receptionprocessors perform reception processing on the extracted signals toacquire frames and output the frames to the receiver 32. The receptionprocessing includes, for example, A/D conversion, demodulationprocessing, and physical layer processing such as analysis of a physicalheader.

The receiver 32 performs analysis or the like of MAC headers of theframes input from the PHY processing and wireless unit 20. Whendetermining from an analysis result of the MAC headers of the receivedframes that the received frames are data frames, the receiver 32 outputsthe data frames to the upper layer processor 40 according to necessity.If the received frames are management frames or control frames, thereceiver 32 outputs the frames to the first controller 33. According towhether the received frames are frames for which an ACK(Acknowledgement) response is necessary and whether the reception of theframes is successful, the receiver 32 outputs a generation instructionfor an ACK frame to the first controller 33 or directly outputs thegeneration instruction to the transmitter 31. The receiver 32 can alsooutput a generation instruction for a BlockAck frame (BA frame) insteadof the ACK frame. The ACK frame and the BlockAck frame are forms of anacknowledgement response frame. The BA frame includes informationrepresenting success or failure of the received frames.

Note that the management frame used for management of a communicationlink between the terminal and the other terminals. Examples of themanagement frame include a beacon frame, an association request frame (aconnection request frame for requesting connection to the base station),and an association response frame (a connection response frame, which isa response frame to the connection request frame). Besides, there isalso a management frame defined anew in this embodiment explained below.The control frame is a frame used for control in transmitting andreceiving (exchanging) the management frame and the data frame betweenthe wireless communication device and the other wireless communicationdevices. Examples of the control frame include an RTS frame, a CTSframe, and an ACK frame. Details of the data frame, the managementframe, and the control frame are explained in below in otherembodiments.

The receiver 32 performs management of carrier sensing information viathe transmission and reception processors of the PHY processing andwireless unit 20. As the carrier sensing information, there are physicalcarrier sensing information concerning busy and idle of a medium (CCA)input from the PHY processing and wireless unit 20 and virtual carriersensing information based on medium reservation time described in thereceived frame. If one of the physical carrier sensing information andthe virtual carrier sensing information indicates busy, the medium isregarded as busy. Transmission of signals is prohibited while the mediumis busy. Note that, in the IEEE802.11 standard, the medium reservationtime is decided to be described in a Duration field (see FIG. 4 referredto below) in the MAC header. When receiving a frame addressed to anotherterminal (i.e., not addressed to the own terminal), the receiver 32determines that the medium is virtually busy during the mediumreservation time described in the frame. Such a mechanism for virtuallydetermining medium busy or a period of the virtual medium busy is calledNAV (Network Allocation Vector).

When the terminal is connected to the base station 101, the terminalgenerates, under the control by the first controller 33, in thetransmitter 31, a connection request frame, that is, an associationrequest frame. As an example of a transmission method of the associationrequest frame, for example, as in IEEE802.11ac, the association requestframe is transmitted in a primary channel commonly recognized in asystem. The association request frame may be transmitted in a pluralityof channels including the primary channel. The primary channel may bedecided beforehand as, for example, the channel 1. The base station canselect and determine the primary channel out of a plurality of channels.Information indicated by the primary channel may be notified to theterminals from the base station 101 by a beacon frame.

The receiver 32 of the terminal receives an association response frame,which is a response to the association request frame from the basestation 101. Consequently, the terminal is connected to the base station101 and belongs to a wireless communication group formed by the basestation 101.

The terminal receives, from the base station 101, notification ofchannels allocated by the base station as channels used in the MU-MCcommunication. The notification is performed by, for example, a beaconframe transmitted from the base station 101, the association responseframe, or a separately defined management frame. When the managementframe includes information designating the channels used in the MU-MCcommunication, the information is notified to the first controller 33.The second controller 34 grasps the notified channels as the channelsused in the MU-MC communication. The configuration of information fornotifying the channels allocated to the terminal may be optional as longas the channel numbers can be specified.

The terminal may notify information concerning channels that the ownterminal requests to use (use requested channel information) to the basestation 101 with a management frame or the like at an association timeor any timing after the association time. The base station 101 maydetermine, on the basis of the use requested channel information,channels used by the terminals.

In this case, the terminal may determine, by performing carrier sensing,the channels that the own terminal desires to use. For example, theterminal performs carrier sensing from the channel 1 to the channel 8via the PHY processing and wireless unit 20. Carrier sensing results inthe channels are notified to the receiver 32 from the PHY processing andwireless unit 20. The first controller 33 selects, on the basis of thecarrier sensor results of the channels, the channels that the terminaldesires to use. For example, when the channels 1 and 2 are busy and thechannels 3 to 8 are idle, the first controller 33 selects the channelsout of the channel 3 to the channel 8. Channel selection conditions suchas the number of channels to be used may be optional. Note that, in thecase of the resource unit-based OFDMA scheme, carrier sensing may beperformed in units of channels. In that case, the first controller 33only has to select, out of channels in which the carrier sensing isidle, a resource unit that the terminal desires to use. Monitoring ofthe primary channel may be performed in the monitoring of the channelseven in the case of the resource unit-based OFDMA.

The first controller 33 controls the transmission and receptionprocessors to perform standby operation in channels for the MU-MCcommunication according to a start notification frame of the MU-MCcommunication received from the base station. The start notificationframe has a form of a beacon frame, a separately defined managementframe, or a control frame. The standby operation means standing by for aframe transmitted from the base station 101 in a receivable state.Specifically, the standby operation may include performing carriersensing in a channel corresponding to the frame and setting theoperation of the transmission and reception processor and the receiverto be capable of performing reception processing such as reception anddemodulation of a signal of the frame in the channel corresponding tothe frame. The start notification frame announces that the MU-MCcommunication is to be started. The start notification frame may have afunction of notifying an MU-MC validity period, which is a period inwhich the MU-MC communication is possible.

Note that the terminal may notify the base station at an associationtime or any timing after the association time that the MU-MCcommunication can be executed and the function of the MU-MCcommunication is enabled (on). The base station may recognize, as aterminal capable of performing the MU-MC communication, the terminalthat performs the notification.

In this embodiment, one of characteristics is to suppress time for theterminal to perform the standby operation in the channels for the MU-MCcommunication and achieve a reduction in power consumption. As anexample, the terminal is caused to perform the standby operation in thechannels for the MU-MC communication in the entire or a part of theMU-MC validity period and basically perform the standby operation inonly the primary channel.

As a specific example, the standby operation in the channels for theMU-MC communication is started at a start time of the MU-MC validityperiod (also referred to as a start time of the MU-MC communication).The standby operation channels are reset to the original channel (theprimary channel) at an end time of the MU-MC validity period (alsoreferred to as an end time of the MU-MC communication). Information forspecifying the start time may be notified from the base station as astart notification frame (a beacon frame, a management frame, etc.). Thestart time may be a value for specifying a specific time or may bespecified as elapsed time from the transmission of the startnotification frame. The start time may be set to a transmission time ofthe start notification frame. Notification of information for specifyingthe start time may be omitted. In this case, after reception of thestart notification frame, the standby operation in the channels for theMU-MC communication only has to be immediately started. Information forspecifying the end time may be notified from the base station as thestart notification frame. The end time may be a value for specifying aspecific time or may be specified as elapsed time from the startnotification frame. After the transmission of the start notificationframe, the end time of the MU-MC validity period may be specified bytransmission times of the beacon frame such as an end time of a beaconinterval immediately before the beacon frame transmitted in an X-thtime. After the transmission of the start notification frame, the MU-MCvalidity period may be set during continuous X times of the beaconinterval and a value of the X may be notified. In this case, when thestart notification frame is the beacon frame, the transmission time ofthe start frame may coincide with the start time of the MU-MC validityperiod. An end time of the last beacon interval (a transmission time ofthe beacon frame) may be equivalent to the end time of the MU-MCvalidity period.

After the reception of the start notification frame, when another startnotification frame is received during the MU-MC validity period, it maybe determined that the MU-MC validity period ends. The standby operationchannels may be reset to the original channel (the primary channel).However, when the own terminal is designated in another startnotification frame as well, the standby operation channels may bemaintained as long as there is no change in the channels for the MU-MCcommunication.

When the standby operation channels are changed, a setup time forchanging or starting the channels is necessary. For example, time foradjusting an operation band of an analog filter according to the changedchannels is necessary. When it is necessary to start an analog filteranew, time for performing power supply and band adjustment to change theanalog filter to an operable state is necessary. When it is necessary tostart digital filters, time for reading out the digital filters from thememory and making the digital filters applicable is necessary.Therefore, in order to make it possible to start the standby operationin the channels for the MU-MC communication at the start time, it isnecessary to start startup operation before the start time and, by thestart time, change the digital filter to a state in which the standbyoperation is possible. Therefore, it is necessary to decide the starttime of the MU-MC validity period such that the change of the standbyoperation channels can be completed until the start time after a targetterminal of the MU-MC communication receives the start notificationframe. When maximum time for the channel change is decided beforehand,the start time may be decided beforehand in the system as a time afterfixed time (>=the maximum time) from the transmission of the startnotification frame. The terminals may notify information representingtimes required for a channel change in the own terminals (setup timeinformation) to the base station, respectively. The base station maydetermine the start time on the basis of a largest time among the timesof the target terminals of the MU-MC communication. As the setup timeinformation of the terminals, values of times required for setup may benotified or stages (levels) may be notified according to a value rangecorresponding to the setup time information among a plurality of valueranges such as 500 is or less or 1 μs or less.

Note that the frame explained in this embodiment is not limited to, forexample, what is called frame in the IEEE802.11 standard and mayindicate what is called packet.

FIG. 3 is a block diagram of the wireless communication device mountedon the base station 101.

The wireless communication device of the base station 101 includes oneor a plurality of antennas, a PHY processing and wireless unit 70, a MACprocessor 80, and an upper-layer processor 90. The MAC processor 80includes a transmitter 81, a receiver 82, a first controller 83, asecond controller 84, and a timer 85. A controller is divided into thefirst controller 83 and the second controller 84. However, the firstcontroller 83 and the second controller 84 may be collected as onecontroller. The MAC processor 80 or a set of the MAC processor 80 andthe PHY processing and wireless unit 70 corresponds to the integratedcircuit for wireless communication in this embodiment. The entire or apart of processing of digital regions of the units or processing of theintegrated circuit for wireless communication may be performed bysoftware (a program) operating in a processor such as a CPU, may beperformed by hardware, or may be performed by both of the software andthe hardware. The base station 101 may include a processor that performsthe entire or a part of the processing of the units.

The PHY processing and wireless unit 70 includes one or a plurality oftransmission and reception processors. When X represents an integerequal to or larger than 1, the PHY processing and wireless unit 70includes first to X-th transmission and reception processors. Antennasare respectively connected to the transmission and reception processors.One transmission and reception processor may be disposed for each onechannel. When a plurality of channels are collectively processed, onetransmission and reception processor may be disposed for the pluralityof channels. When one transmission and reception processor is disposedfor each one channel, if the wireless communication device is adaptableup to eight channels, the PHY processing and wireless unit 70 includeseight transmission and reception processors in order to performprocessing for each one channel. In an example shown in the figure, theantenna is connected to each of the transmission and receptionprocessors. However, one antenna may be connected to the plurality oftransmission and reception processors in common. In this case, thetransmission and reception processors, to which one antenna is connectedin common, only have to extract signals of channels respectivelyallocated to the own processors. The transmission and receptionprocessors may extract signals for all channel bands with an analogfilter covering all or a plurality of channels and extract signals ofchannels of the own processor with digital filters or may extractsignals with an analog filter corresponding to only a channel band ofthe own processor. An operation band of the analog filter may bevariable according to an instruction of the second controller 34. Theanalog filter may have an operating band that is variable according todesignation by the controller 34, or may be capable of supporting onlysignals in a preliminarily fixed band. Concerning transmission, thetransmission and reception processors may respectively correspond toseparate channels or may correspond to all or a plurality of channels.Information concerning channels allocated to the transmission andreception processors is managed by the second controller 84. The secondcontroller 84 allocates channels to be processed to the transmission andreception processors and indicates the allocated channels to thetransmission and reception processors. The transmission and receptionprocessors process the channels indicated by the second controller 84.

The transmission and reception processors of the PHY processing andwireless unit 70 convert signals received via the antennas from wirelessfrequencies into basebands and extract signals of channels correspondingto the basebands from baseband signals. The transmission and receptionprocessors perform reception processing on the extracted signals toacquire frames and output the frames to the receiver 82. The receptionprocessing includes, for example, A/D conversion, demodulationprocessing, and physical layer processing such as analysis of a physicalheader.

The receiver 82 performs analysis or the like of MAC headers of theframes input from the PHY processing and wireless unit 70. Whendetermining from an analysis result of the MAC headers of the receivedframes that the received frames are data frames, the receiver 82 outputsthe data frames to the upper layer processor 90 according to necessity.If the received frames are management frames or control frames, thereceiver 32 outputs the frames to the first controller 83. According towhether the received frames are frames for which an ACK(Acknowledgement) response is necessary and whether the reception of theframes is successful, the receiver 32 outputs a generation instructionfor an ACK frame to the first controller 83 or directly outputs thegeneration instruction to the transmitter 81. Like the receiver 32 ofthe terminal, the receiver 82 performs management of carrier sensinginformation. As explained above, the carrier sensing information mayinclude both of physical carrier sensing information and virtual carriersensing information.

The first controller 83 manages an access to a channel and controlstransmission of a frame at desired timing. The first controller 83 mayuse the timer 85 in order to perform the frame transmission at thedesired timing. The first controller 83 sets a time period until a timeof the desired timing in the timer 85. When the timer 85 times out, thefirst controller 83 executes frame transmission. The first controller 83includes allocator for allocating channels to the terminals for theMU-MU communication. The first controller 83 allocates the channels tothe terminals using the allocator. The first controller 83 manages thechannels allocated to the terminals. The first controller 83 mayallocate the channels to the terminals according to any method. Forexample, when the first controller 83 receives use requested channelinformation from the terminals, the first controller 83 allocates thechannels to the terminals on the basis of the information. Basically,the first controller 83 allocates the channels to the terminals not tooverlap. However, the channels to be allocated may overlap among theterminals. During actual MU-MC communication, the first controller 83may control the channels overlapping among the terminals not to be used.As a method of not using the use requested channel information, thefirst controller 83 may determine, on the basis of data amountsaddressed to the terminals, channels to be allocated to the terminals.

The first controller 83 instructs the transmitter 81 to generate andtransmit a frame including information for notifying the channelsallocated to the terminals. As explained above, as the frame fornotifying the information, there are an association response frame, abeacon frame, and other management frames. When determining a start ofthe MU-MC communication considering that, for example, data addressed toa plurality of terminals are present, the first controller 83 determinesa terminal set as a target of the MU-MC communication. The firstcontroller 83 instructs the second controller 84 to change standbyoperation channels of the own station to channels used in the MU-MCcommunication. Note that the standby operation may be performed in theprimary channel even if the primary channel is not used in the MU-MCcommunication. The first controller 83 instructs the transmitter 81 togenerate a frame for notifying the start of the MU-MC communication (astart notification frame) and transmit the start notification frame inthe primary channel. For example, information for specifying adesignated terminal is included in the start notification frame.Information for specifying the channel allocated to the terminal canalso be included in the start notification frame. Besides, informationfor specifying a start time of an MU-MC validity period, information forspecifying an end time, or a combination of these kinds of informationmay be included

The first controller 83 and the second controller 84 may access astorage device and read out information to be transmitted to theterminal. The first controller 83 and the second controller 84 may storeinformation received from the terminal in the storage device. Thestorage device may be a buffer (an internal memory) included in thefirst controller 83 or the second controller 84 or both of thecontrollers or may be a buffer (an external memory) provided on theoutside of the first controller 83 or the second controller 84. Thestorage device may be a volatile memory such as a DRAM or may be anonvolatile memory such as a NAND or a MRAM. Besides the memories, thestorage device may be an SSD, a hard disk, or the like.

The transmitter 81 performs generation and transmission of frames (amanagement frame, a control frame, and a data frame) under the controlby the first controller 83. When generation and transmission of a frameare instructed from the first controller 83, the transmitter 81generates the designated frame and outputs the generated frame to thePHY processing and wireless unit 70. When the frame to be transmitted isthe data frame, data stored in a body field of the data frame is dataacquired from the upper-layer processor 40. The PHY processing andwireless unit 70 inputs the frame generated by the transmitter 81 to thetransmission and reception processor corresponding to the frame. Thetransmission and reception processors perform processing of a desiredphysical layer on the frame input from the transmitter 81 to generate aphysical packet, perform D/A conversion, frequency conversion, and thelike on the physical packet to generate a signal having a radiofrequency, and transmit the signal from the antenna to the space as aradio wave.

A basic format example of the frame in this embodiment is shown in FIG.4.

The frame format shown in FIG. 4 includes fields of a MAC header, aframe body, and an FCS (Frame Check Sequence). The data frame, themanagement frame, and the control frame are basically based on theformat. A part of the fields is sometimes omitted as appropriate. Theassociation request frame, the association response frame, the beaconframe, and the like explained above are also the management frame.Therefore, the frames also have this frame format.

The MAC header includes fields of Frame Control, Duration, Address 1,Address 2, Address 3, Sequence Control, Address 4, QoS Control, HT (HighThroughput) control, and MU-MC information. A destination address(Receiver Address; RA) is set in the field of Address 1. A transmissionsource address (Transmitter Address; TA) is set in the field of Address2. A BSSID (Basic Service Set Identifier) (in some case, a wildcardBSSID targeting all BSSIDs by setting 1 in all bits), which is anidentifier of a BSS, or a TA is set in the field of Address 3 accordingto a use of the frame. The field of Address 4 is used, for example, inthe case of communication between base stations.

In the management frame, information inserted into the frame body ismanaged as an information element. A format example of the informationelement is shown in FIG. 5(A). The information element includes anElement ID field, a Length field, and an Information field. A value foridentifying the information element is stored in the Element ID field.Information to be notified is stored in the Information field(hereinafter, information field). Length information of the informationfield is stored in the Length field. In the frame body field, one or aplurality of the information element having such a configuration can bestored.

An MU-MC information field is a field for notifying presence or absenceof a start of the MU-MC communication and is a field defined anew inthis embodiment. As an example, a bit “1” is set when the start of theMU-MC communication is notified and a bit “0” is set otherwise. A frameof the bit “1” is equivalent to the start notification frame. Meaningsof the bits may be opposite. When the start of the MU-MC communicationis notified, information for specifying a terminal set as a target ofthe MU-MC communication (terminal specifying information) is set in theframe body field. Specifically, a new information element for the startnotification of the MU-MC communication is defined. The terminalspecifying information is notified by the information element. Theinformation element is referred to as MU-MC communication startnotification element. A new number is given to the information elementfor an Element ID.

A format example of the MU-MC communication start notification elementis shown in FIG. 5(B). In the Information field, terminal specifyinginformation of one or a plurality of terminals (in the figure, Nterminals are designated by STA info 1 to STA Info N fields) is set. Theterminal specifying information may be an association ID (AID), may be aMAC address, or may be other values capable of uniquely distinguishingthe terminals. The AID is an ID allocated by the base station when theterminals are allocated to the base station. The AID is notified to theterminals beforehand by an association response frame or the like. Agroup ID may be used as the terminal specifying information. In thiscase, it is assumed that the base station groups the terminals at anassociation time with the terminals or any timing after the associationtime and notifies group IDs of groups respectively belonging to theterminals. In addition to the terminal specifying information,information for specifying channels that the base station causes theterminals to use may be added to the STA Info 1 to STA Info N fields.Another information element may be defined. The information forspecifying the channels may be notified by the information element ormay be notified by other methods.

Besides notifying the start of the MU-MC communication using the MU-MCInformation field shown in FIG. 4, it is also possible to notify thestart of the MU-MC communication using a frame format in which the MU-MCinformation field is absent. This frame format is shown in FIG. 6(A).The start of the MU-MC communication may be notified using, for example,a null bit (a bit in a Reserved field) of an HT Control field of theframe format. A format example of the HT Control field is shown in FIG.6B. As an example, the start of the MU-MC communication can be notifiedusing a bit in a null field of an HT control Middle subfield.

In the example explained with reference to FIGS. 4 to 6B, the start ofthe MU-MC communication, the designation of the terminal, and the likeare performed using the MAC header and the body field of the MAC frame.However, it is also possible to use a physical header (PHY header) addedto the head side of the MAC frame. As shown in FIG. 7, an MU-MCInformation field and terminal specifying information fields (STA Info 1to STA Info N) for a plurality of terminals are disposed in the physicalheader. The PHY header includes, in addition to these fields, an L-STF(Legacy-Short Training Field), an L-LTF (Legacy-Long Training Field),and an L-SIG (Legacy Signal Field). The L-STF, L-LTF, and L-SIG arefields capable of recognizing terminals of legacy standards such asIEEE802.11a. Information such as signal detection, frequency correction,and transmission speed are stored in the fields.

Several examples of an operation sequence related to the MU-MCcommunication between a base station and a plurality of terminals areexplained with reference to FIGS. 8 to 11.

FIG. 8 shows an example of the operation sequence of the base stationand the plurality of terminals. The base station includes data addressedto terminals 1, 2, and 4. The operation sequence is a sequence intransmitting the data using the MU-MC communication. The horizontal axisrepresents time and the vertical axis represents channels 1 to 8. Theterminals 1, 2, and 4 are capable of executing the MU-MC communication.The function of the MU-MC communication is enabled (on) in the terminals1, 2, and 4.

Hatched rectangles mean frames transmitted by the base station. Whiterectangles mean frames transmitted by the terminals other than the basestation. Rectangles with “B” represent beacon frames. Rectangles with“R” represent RTS frames. The numerals on the right side of “R”represent terminal numbers at destinations of the RTS frames. Forexample, “R1” represents the RTS frame addressed to the terminal 1. “C”represents a CTS frame. “DATA” represents a data frame. “A” representsan ACK frame (an acknowledgement response frame).

Note that, when the base station transmits a plurality of frames to theplurality of terminals, the plurality of frames to be transmitted may bethe same or may be different. When the base station is represented astransmitting or receiving a plurality of frames or a plurality of X-thframes as general representation, the frames or the X-th frames may bethe same or may be different. Any value can be set in X according to asituation.

The base station transmits a beacon frame at a fixed cycle. When thebase station performs the MU-MC communication, the base station notifiesa start of the MU-MC communication using the beacon frame as the startnotification frame. In the example shown in the figure, the base stationnotifies a start of an MU-MC validity period with a beacon frame 601.Information representing the start of the MU-MC communication andinformation for specifying terminals that perform the MU-MCcommunication (terminal specifying information) are included in thebeacon frame 601. Since the terminals 1, 2, and 4 are targets of theMU-MC communication, the beacon frame 601 includes information forspecifying the terminals 1, 2, and 4. Information designating channelsused by the terminals 1, 2, and 4 in the MU-MC communication may beincluded in the beacon frame 601. The information is included in thebeacon frame 601. In this example, the channels 1 and 2 are designatedfor the terminal 1, the channels 4 to 7 are designated for the terminal2, and the channels 5 to 7 are designated for the terminal 4. Theterminals receive the beacon frame 601, analyze the beacon frame 601,and grasp a start time and an end time of the MU-MC validity period. Inthis example, it is assumed that the start time is decided beforehand asa time after fixed time from reception of the beacon frame. Theterminals determine that a period of a beacon interval from the beaconframe 601 until reception of the next beacon frame 602 is the MU-MCvalidity period. That is, the terminals grasp that an end time of thebeacon interval is the end time of the MU-MC validity period. It isassumed that this is recognized in common beforehand by the base stationand the terminals.

The base station stays on standby for a period 611, which ispredetermined time or time having length equal to or longer than thepredetermined time, from the transmission of the beacon frame 601 anddetects arrival of the start time. In order to perform the MU-MCcommunication with the terminals 1 and 2 among the terminals 1, 2, and4, the base station transmits the RTS frames in the channels 1 and 2corresponding to the terminal 1 and the channels 4 to 7 corresponding tothe terminal 2. In this case, the base station performs, in the channels1, 2, and 4 to 7, carrier sensing between a DIFS and back-off timedetermined at random and confirms that a carrier sensing result is idleto acquire an access right, that is, time in which a medium can beoccupied (TXOP). A destination address (RA) of the RTS framestransmitted to the terminal 1 is a MAC address of the terminal 1. Atransmission source address (TA) of the RTS frames is a MAC address ofthe base station. Both of the RTS frames transmitted in the channels 1and 2 are frames having the same content (Duplicate frames).Transmission of the frames having the same content is sometimes referredto as Duplicate transmission. A destination address of the RTS frametransmitted to the terminal 2 is a MAC address of the terminal 2. Atransmission source address of the RTS frame is the MAC address of thebase station. The RTS frames transmitted in the channels 4 to 7 are theDuplicate frames.

It is assumed that the terminals connected to the base station areperforming the standby operation in the channel 1, which is the primarychannel, during normal operation and the channels 2 to 8 are turned offto reduce power consumption. When the transmission and receptionprocessors (see FIG. 2) are present for the respective channels, forexample, the transmission and reception processor corresponding to thechannel 1 may be turned on (ON) and the other transmission and receptionprocessors may be turned off (OFF). When a plurality of channels arecovered by one transmission and reception processor, an analog filtermay be set to cover a band of the channel 1 and block bands of the otherchannels. For example, the operation of the analog filter is set in acenter frequency of the filter and a range from the center frequency,the center frequency only has to be set to a center frequency of thechannel 1 and the range only has to be set to a value corresponding tothe width of the channel 1. When all the channels are covered by oneanalog filter and the respective channels are processed by digitalfilters, the digital filters for the channels other than the channel 1only have to be stopped. Consequently, a reduction in power consumptioncan be achieved by eliminating operation for performing receptionprocessing such as demodulation of frames of the channels other than thechannel 1.

In order to change the channels for the standby operation, as explainedabove, the terminals need the setup time. The terminals 1, 2, and 4respectively receive beacon frames 601 and analyze the beacon frames601. Consequently, the terminals 1, 2, and 4 detect that the ownterminals are designated as targets of the MU-MC communication anddetect channels designated for the own terminals as channels for theMU-MC communication. The terminals 1, 2, and 4 respectively switch thestandby operation channels to the channels for the MU-MC communication.That is, the terminal 1 sets the channels 1 and 2 as the standbyoperation channels. The terminal 2 sets the channels 4 to 7 as thestandby operation channels. The terminal 4 sets the channels 5 to 7 asthe standby operation channels. Note that the channel 1, which is theprimary channel, may be always set as the operation channel. The standbyoperation may be performed in the channel 1.

Time until the start time of the MU-MC validity period after thetransmission of the beacon frame 601 by the base station (time in whichthe base station stays on standby until the base station is enabled totransmit the RTS frames to the terminals 1 and 2) is set to the longesttime among the set up times of the terminals that perform the MU-MCcommunication or time longer than the longest time.

Note that the base station may secure a TXOP (an access right) at leastduring the predetermined time using the Duration field of the beaconframe 601 such that the RTS frames in the channel 1, which is theprimary channel, can be surely transmitted after standby for thepredetermined time.

The terminals 1 and 2 receive the RTS frame transmitted from the basestation and transmit CTS frames in channels in which a carrier sensingresult is idle for fixed time (PIFS) before the reception. The terminal1 receives the RTS frames in the channels 1 and 2 and the carriersensing result is idle for the fixed time (PIFS) before the reception.Therefore, the terminal 1 transmits the CTS frames in the channels 1 and2. The terminal 2 receives the RTS frames in the channels 4 to 7 and thecarrier sensing result is idle for the fixed time (PIFS) before thereception. Therefore, the terminal 2 transmits the CTS frames in thechannels 4 to 7. Note that, if there is a channel in which the RTS framecannot be received or a channel that is busy for the PIFS time beforethe reception, the CTS frame is not returned in the channel. Adestination address (RA) of the CTS frames transmitted from theterminals 1 and 2 is the MAC address of the base station. Note that,since the terminal 4 is performing the standby operation in the channels5 to 7, the terminal 4 can receive the RTS frames transmitted from thebase station in the channels 5 to 7. However, since a destination of theRTS frames is the terminal 2, the terminal 4 determines that the RTSframes are not frames addressed to the own terminal and discards the RTSframes.

After elapse of an SIFS from reception completion of the CTS frames, thebase station transmits data frames in the channels in which the CTSframes are received. The base station receives the CTS framesrespectively in the channels 1 and 2 from the terminal 1 and receivesthe CTS frames in channels 4 to 7 from the terminal 2. Therefore, thebase station simultaneously transmits data frames to the terminal 1 inthe channels 1 and 2 and to the terminal 2 in the channels 4 to 7. It isassumed that the length of time for transmitting the data frames isdetermined beforehand. A plurality of frames may be transmitted or anaggregation frame (a super frame) including a plurality of data framesmay be transmitted. Data frames may be separately transmitted in thechannels 1 and 2. One or a plurality of frames or the aggregation framemay be transmitted to the terminal by binding and using the channels 1and 2 as one band. Similarly, one or a plurality of data frames may betransmitted to the terminal 2 by binding and using the channels 4 to 7as one band. A transmission source address (TA) of the data framestransmitted to the terminal 1 is the MAC address of the base station. Adestination address (RA) of the data frames is the MAC address of theterminal 1. A transmission source address (TA) of the data framestransmitted to the terminal 2 is the MAC address of the base station. Adestination address (RA) of the data frames is the MAC address of theterminal 2.

The terminals 1 and 2 determine on the basis of FCSs of the data framesreceived from the base station whether the reception is successful andreturn ACK frames in channels in which the reception is successful. Theterminal 1 has succeeded in the reception of the data frames in both ofthe channels 1 and 2. Therefore, the terminal 1 returns ACK frames inthe respective channels 1 and 2. The terminal 2 has succeeded in thereception of the data frames in all of the channels 4 to 7. Therefore,the terminal 2 returns ACK frames in the respective channels 4 to 7. Forexample, when the aggregation frame is received, the terminals 1 and 2transmit BA (Block ACK) frames instead of the ACK frames.

After the MU-MC communication with the terminals 1 and 2 is completed,subsequently, in order to perform the MU-MC communication with theterminals 1 and 4, the base station transmits RTS frames to the terminal1 in the channels 1 and 2 and transmits RTS frames to the terminal 4 inthe channels 5 to 7. As explained above, before the transmission, thebase station acquires a TXOP on the basis of carrier sensing between aDIFS and a back-of time. The terminal 1 receives the RTS frames in thechannels 1 and 2. However, it is assumed that a carrier sensing resultfor a PIFS before the reception of the RTS frame is idle in the channel1 and is busy for the PIFS before the reception of the RTS frame.Therefore, the terminal 1 transmits a CTS frame to the base station onlyin the channel 1. The terminal 4 receives RTS frames in the respectivechannels 5 to 7 and all the channels are idle for the PIFS before thereception. Therefore, the terminal 4 transmits CTS frames in therespective channels 5 to 7. Note that the terminal 2 can receive RTSframes in the channels 5 to 7. However, since a destination of the RTSframes is the terminal 4, the terminal 2 determines that the RTS framesare not frames addressed to the own terminal and discards the RTSframes.

The base station receives a CTS frame from the terminal 1 in the channel1 and receives CTS frames from the terminal 4 respectively in thechannels 5 to 7. Therefore, the base station simultaneously transmits adata frame to the terminal 1 in the channel 1 and data frames to theterminal 2 in the channels 5 to 7. A plurality of data frames may betransmitted or an aggregation frame including a plurality of data framesmay be transmitted. Data frames may be separately transmitted to theterminal 2 in the channels 5 to 7. One or a plurality of data frames oran aggregation frame may be transmitted by binding and using thechannels 5 to 7 as one band.

The terminals 1 and 4 determine on the basis of FCSs of the data framesreceived from the base station and return ACK frames in channels inwhich the reception is successful. The terminal 1 has succeeded in thereception of the data frame. Therefore, the terminal 1 returns the ACKframe in the channel 1. The terminal 4 has succeeded in the reception ofthe data frames in all of the channels 5 to 7. Therefore, the terminal 4returns the ACK frames in the respective channels 5 to 7. For example,when the aggregation frame is received, the terminals 1 and 4 transmitBA (Block ACL) frames instead of the ACK frames.

Thereafter, the base station transmits the next beacon frame 602. TheMU-MC validity period ends at an end time of a beacon intervalimmediately before the transmission of the beacon frame 601. Theterminals designated as the targets of the MU-MC communication in thebeacon frame 601 reset the standby operation channels to the originalchannel (the channel 1) according to the end of the beacon intervalstarting in the beacon frame 601. However, when information notifyingthe start of the MU-MC communication again is included in the beaconframe 602 and the own terminals continue to be designated, if there isno change in the standby operation channels, the terminals may maintainthe present channel without resetting the standby operation channels tothe original channel.

In the sequence shown in FIG. 8, the base station stays on standby inthe period 611 after the transmission of the beacon frame 601. However,the base station may perform other communication in the period. Asequence example of the communication is shown in FIG. 9. FIG. 9 isdifferent from FIG. 8 in that the base station performs unicastcommunication with the terminal 3 after transmission of the beacon frame601 and before a start of the MU-MC validity period (before transmissionof the RTS frames). It is assumed that the terminal 3 is not designatedas a target of the MU-MC communication in the beacon frame 601 and iscaused to perform the standby operation only in the channel 1.

After transmitting the beacon frame 601, the base station performscarrier sensing, acquires an access right, and transmits a data frame tothe terminal 3. “D3” represents the data frame addressed to the terminal3. The base station performs the carrier sensing for fixed time andback-off time and, if a carrier sensing result is idle, acquires theaccess right and transmits the data frame. The fixed time is a DIFS, anAIFS, or the like but may be other values. After transmitting the dataframe, the base station receives an ACK frame from the terminal 3 afteran SIFS. Thereafter, when a start time of the MU-MC validity periodarrives, as in FIG. 8, the base station transmits RTS frames to theterminal 1 in the channels 1 and 2 and transmits RTS frames to theterminal 2 in the channels 4 to 7. Consequently, it is possible toeffectively use standby time until the MU-MC communication is actuallystarted. It is possible to improve system efficiency.

The base station performs the terminal 3 not designated in the beaconframe 601. However, the base station can also perform communication withat least one of the terminals 1, 2, and 4 designated in the beacon frame601 if the terminals are performing the standby operation in the channel1. The base station may perform broadcast communication or multicastcommunication rather than the unicast communication. The base stationperforms communication in the channel 1, which is the primary channel,for the standby time. However, if a terminal performing the standbyoperation in another channel is present, the base station may performcommunication in the other channel.

In the above explanation, the start notification of the MU-MCcommunication, the designation of the terminal set as the target of theMU-MC communication, and the like are performed using the beacon frame.A sequence in which a separately defined dedicated management frame isused rather than the beacon frame is explained. In FIG. 10, an exampleof an operation sequence in which a management frame defined anew isused is shown. A rectangle with “M” represents the management frame.Note that it is possible to distinguish according to values of a typeand a sub-type of a Frame Control field whether, for example, themanagement frame is the beacon frame or the separately defined newmanagement frame.

As shown in FIG. 10, when determining execution of the MU-MCcommunication, the base station transmits a management frame 801 fornotifying a start of the MU-MC communication. The management frameperforms carrier sensing between a DIFS and back-off time and, if acarrier sensing result is idle, acquires an access right and transmitsthe management frame 801. Note that, in the case of the beacon frameexplained above, the base station performs similar carrier sensing,acquires an access right, and transmits the beacon frame.

Information for specifying a terminal designated as a target of theMU-MC communication (terminal specifying information) is included in themanagement frame 801. Further, information for specifying channels thatthe base station causes the terminals to use may be included in themanagement frame 801. The base station designates the terminals 5, 3,and 7 and designates the channels 1, 3 to 4, and 6 to 7 respectively forthe terminals 5, 3, and 7. Since the management frame 801 itself has afunction of notifying the start of the MU-MC communication, a field fornotification like the MU-MC information field shown in FIG. 4 does nothave to be included in the management frame 801. However, the field fornotification may be explicitly included in the management frame 801. Asexplained above, the terminal specifying information may be an AID(Association ID), may be a MAC address, or may be a group ID. When thegroup ID is used, for example, a group ID of a group to which theterminals 5, 3, and 7 belong in common is included in the managementframe 801. There is an advantage that it is possible to further reduceinformation size than when the AID, the MAC address, or both of the AIDand the MAC address are designated for the respective terminals.

In the management frame 801, as in the beacon frame, information forspecifying a start time or an end time of the MU-MC validity period maybe included. The start time or the end time may be determined beforehandin a system or a standard without including information for explicitlyspecifying the start time or the end time in the management frame 801.For example, a period from immediately after the transmission of themanagement frame 801 to before the transmission of the next beacon framemay be defined as the MU-MC validity period. The MU-MC validity periodmay be defined by any method if the MU-MC validity period is recognizedin common between the base station and the terminals beforehand.

The terminals 5, 3, and 7 receive and analyze the management frame 801transmitted from the base station to recognize that the own terminalsare designated as targets of the MU-MC communication. The terminals 5,3, and 7 switch the standby operation channels to channels for the MU-MCcommunication. Since the channel 1, which is the primary channel, is achannel for the MU-MC communication, the terminal 5 maintains thepresent channel. The terminal 3 switches the standby operation channelsto the channels 3 and 4. The terminal 7 switches the standby operationchannels to the channels 6 and 7. Note that the base station only has tocause the terminals 3 and 7 to continue the standby operation concerningthe channel 1, which is the primary channel.

After staying on standby for predetermined time that takes into accountchannel setup times in the terminals 5, 3, and 7, the base stationtransmits RTS frames respectively to the terminals 5, 3, and 7 in thechannels 1, 3 to 4, and 6 to 7. The terminals 5, 3, and 7 receive theRTS frames respectively in the channels 1, 3 to 4, and 6 to 7. Carriersensing is idle in all of the channels 1, 3 to 4, and 6 to 7 for a PIFSbefore reception. Therefore, the terminals 5, 3, and 7 return CTS framesrespectively in the channels 1, 3 to 4, and 6 to 7.

The base station receives the CTS frames from the terminals 5, 3, and 7in the channels 1, 3 to 4, and 6 to 7. Therefore, the base stationsimultaneously transmits data frames to the terminals 5, 3, and 7 in thechannels 1, 3 to 4, and 6 to 7. The terminal 1 normally receives thedata frame from the base station in the channel 1 and returns an ACKframe. The terminal 3 normally receives the data frame in the channel 3of the channels 3 and 4 and fails in the reception in the channel 4.Therefore, the terminal 3 returns an ACK frame only in the channel 3.The terminal 7 normally receives the data frame in the channel 6 of thechannels 6 and 7 and fails in the reception in the channel 7. Therefore,the terminal 7 returns an ACK frame only in the channel 3.

Note that, as in the case of the sequence example in which the beaconframe is used, a plurality of channels may be bound and used as oneband. An aggregation frame including a plurality of data frames may betransmitted. BA frames may be used instead of the ACK frames.

FIG. 11 shows an operation sequence example in which both of a beaconframe and a management frame are combined to control the MU-MCcommunication.

First, the base station transmits a beacon frame 901 in the channel 1,which is the primary channel, to notify a start of the MU-MCcommunication. In the beacon frame 901, the base station designates theterminals 1 and 2 as targets of the MU-MC communication. After stayingon standby for a predetermined period that takes into account setuptimes in the terminals 1 and 2, the base station transmits RTS frames tothe terminals 1 and 2 respectively in the channels 1 and 2 and 4 to 7.Thereafter, a sequence from reception of RTS frames in the terminals 1and 2 to transmission and reception of CTS frames, data frames, and ACKframes is the same as the sequence example shown in FIG. 11.

After the communication with the terminals 1 and 2, in order to performthe MU-MC communication with the terminals 1 and 4, the base stationtransmits a management frame 903 halfway in the present beacon interval.In the management frame 903, the base station designates the terminals 1and 4 as targets of the MU-MC communication. Since the terminal 1 isalready designated in the beacon frame 901, the designation may beomitted in the management frame 901 (e.g., when an MU-MC validity periodnotified in the beacon frame 901 is validity before transmission of thenext beacon frame 902).

The base station may regard the MU-MC validity period by a beacon frame(or another management frame) before transmission of the managementframe 903 as being forcibly finished by the transmission of themanagement frame 903. In this case, when the same terminal continues tobe designated, the base station only has to designate the terminal (theterminal 1) in the management frame 903 again. The terminal (theterminal 2) not designated again in the management frame may operate toreset the standby operation channels to the original channel (thechannel 1) at a point in time when the terminal detects that the ownterminal is not designated in the management frame. Since the terminal 1continues to be designated, the present channel only has to continue tobe used as the standby operation channel.

Alternatively, in the beacon frame 901, the base station may designate atime before a transmission scheduled time of the management frame 903 asan end time of the MU-MC validity time. The terminals 1 and 2 maydetermine that the MU-MC validity period ends at the end time and resetthe standby operation channels to the original channel. In this case,taking into account time required until the standby operation channelsare reset to the original channel, the base station may transmit themanagement frame 903 after at least the terminal (the terminal 1) to becontinuously designated is reset to the original channel.

The operation of the base station performing the MU-MC communicationafter transmitting the management frame 903 is the same as the operationsequence example of the MU-MC communication with the terminals 1 and 4in FIG. 8.

In the operation sequence example shown in FIG. 11, the terminal 4 onlyhas to perform a change of the standby operation channel after receivingthe management frame 903. Therefore, channel standby operation time isshorter than when the change of the standby operation channel isperformed at a point in time when the beacon frame 901 is received as inthe sequence shown in FIG. 8. Therefore, it is possible to reduce powerconsumption of the terminal 4.

In the sequence examples shown in FIGS. 8 to 11, the base station maynotify, in the beacon frame or the management frame, channels used bythe terminals in the MU-MC communication or may notify the channels tothe terminals beforehand at the association time or the like. In thiscase, when the own terminals are designated in the beacon frame or themanagement frame, the terminals only have to switch the channels tochannels for the MU-MC communication grasped beforehand and perform thestandby operation. Note that the channel 1, which is the primarychannel, may be always operated even if the channel 1 is not a channelfor the MU-MC communication.

The terminals may grasp, during the reception of the RTS frames, thechannels used in the MU-MC communication. In this case, when the ownterminals are designated in the beacon frame or the management frame,the terminals wait for frames in all channels (e.g., all of the channels1 to 8) that are likely to be used in the MU-MC communication. Theterminals only have to grasp, as channels for the MU-MC communication ofthe own terminals, channels in which RTS frames addressed to the ownterminals are received and return CTS frames in channels that are idlein a PIFS before the reception of the RTS frames. Even in this case, theterminals only have to set only the channel 1, which is the primarychannel, as the standby operation channel until being notified of thestart of the MU-MC communication and, after the notification of thestart is received, extend the standby operation channel to the channels1 to 8. Therefore, it is possible to obtain a reduction effect of powerconsumption.

Setting examples of filters for reception (analog filters and digitalfilters) of the base station and the terminal after the MU-MCcommunication start notification are explained with reference to FIGS.12(A) to 16(B). The operation of filter setting is explained withreference to the terminal 2 as an example. The same applies to the otherterminals.

FIG. 12(A) shows a setting example of an analog filter and digitalfilters of the base station. FIG. 12(B) shows a setting example of ananalog filter and digital filters of the terminal 2. Note that, in thisexample, the base station transmits one or a plurality of data frames oran aggregation frame using, for each of the terminals, channels for theMU-MC communication as a band obtained by binding the channels. Theterminals transmit BA frames in the channels (note that it is alsopossible to return BA frames when one data frame is transmitted).Contents of the BA frames transmitted in the channels for each of theterminals are the same. Rectangles with “BA” represent the BA frames.Rectangles with characters “DATA” extending over a plurality of channelsrepresent data frames or aggregation frames transmitted in a bandobtained by bundling the plurality of channels.

As shown in FIG. 12(A), in the base station, an analog filter 1001 isset to cover all of the channels 1 to 8. The base station processes, indigital filters 1001 a, 1001 b, 1001 c, 1001 d, 1001 e, and 1001 f forthe respective channels, signals passed through the analog filter 1001to extract signals of the respective channels. In this example, the basestation extracts, for the respective channels, digital signals of thechannels 1 and 2 for the terminal 1, the channels 4 and 5 for theterminal 2, and the channels 7 and 8 for the terminal 3.

As shown in FIG. 12(B), in the terminal 2, an analog filter 1002 is setto cover all of the channels 1 to 8. The terminal 2 processes, indigital filters 1002 b and 1002 c for the respective standby operationchannels (the channels 4 and 5), signals passed through the analogfilter 1002 to extract digital signals of the respective channels. Inthis example, the terminal 2 monitors the channel 1, which is theprimary channel, as well during the MU-MC validity period. The terminal2 processes a signal passed through the analog filter 1002 in a digitalfilter 1002 a corresponding to the channel 1 to extract a digital signalof the channel 1 as well.

FIG. 13A shows another setting example of the analog filter and thedigital filters of the base station. FIG. 13(B) shows another settingexample of the analog filter and the digital filters of the terminal 2.Explanation overlapping the explanation of FIGS. 12(A) and 12(B) isomitted.

As shown in FIG. 13(A), in the base station, an analog filter 1101covering the channels 1 and 2 for the terminal 1, an analog filter 1102covering the channels 4 and 5 for the terminal 2, and an analog filter1103 covering the channels 7 and 8 for the terminal 3 are set. Filteringconcerning the other channels is turned off. The base station processes,in digital filters 1101 a and 1101 b for the respective channels 1 and2, signals passed through the analog filter 1101 to extract signals ofthe channels 1 and 2. The base station processes, in digital filters1102 a and 1102 b for the respective channels 4 and 5, signals passedthrough the analog filter 1102 to extract signals of the channels 4 and5. Similarly, the base station processes, in digital filters 1103 a and1103 b for the respective channels 7 and 8, signals passed through theanalog filter 1103 to extract signals of the channels 7 and 8.

As shown in FIG. 13(B), in the terminal 2, an analog filter 1105covering the channels 4 and 5 for the MU-MC communication and an analogfilter 1106 of the channel 1, which is the primary channel, are set. Theterminal 2 processes, in digital filters 1105 a and 1005 b for therespective channels 4 and 5, signals passed through the analog filter1105 to extract signals of the channels 4 and 5. The terminal 2 extractsa signal of the channel 1 in the analog filter 1106 of the channel 1.Note that, in a period other than the MU-MC validity period, an analogfilter of the channel 1, which is the primary filter, is set. Theterminal 2 receives a beacon frame and the like from the base station.

FIG. 14(A) shows another setting example of the analog filter of thebase station. FIG. 14(B) shows another setting example of the analogfilter of the terminal 2. Differences from FIGS. 13(A) and 13(B) areexplained below.

As shown in FIG. 14(A), the base station sets analog filters forrespective channels used in the MU-MC communication in the MU-MCvalidity period. Specifically, the base station sets analog filters1201, 1202, 1203, 1204, 1205, and 1206 respectively for the channels 1,2, 4, 5, 7, and 8. As shown in FIG. 14(B), the terminal 2 sets analogfilters 1207 and 1208 respectively for the channels 4 and 5 used in theMU-MC communication. The terminal 2 sets an analog filter 1209 for thechannel 1, which is the primary channel. Consequently, both of the basestation and the terminal 2 extract signals for desired channels withoutusing digital filters.

FIG. 15(A) shows another setting example of the analog filter and thedigital filters of the base station. FIG. 15(B) shows another settingexample of the analog filter and the digital filters of the terminal 2.

As shown in FIG. 15(A), in the MU-MC validity period, the base stationsets an analog filter 1201 covering the channels 1 and 2 for theterminal 1 and an analog filter 1202 covering the channels 4 to 7 forthe terminal 2. As shown in FIG. 15(B), in the MU-MC validity period,the terminal 2 sets an analog filter 1204 covering the channels 4 to 7.Note that, in this example, the terminal 2 sets an analog filter 1203for the channel 1 in a period other than the MU-MC validity period.However, the terminal 2 releases the setting of the analog filter of thechannel 1 in the MU-MC validity period (does not perform the standbyoperation in the channel 1). The terminal 2 extracts a signal in theanalog filter 1204 and extracts signals in digital filters 1204 a, 1204b, 1204 c, and 1204 d for the respective channels 4 to 7 to receive RTSframes for the respective channels. It is assumed that the terminal 2determines that the RTS frames are normally received in the channels 6and 7 but a carrier sensing result is busy in an PIFS period beforereception in the channel 5 and reception fails in a CRC (CyclicRedundancy Check) inspection in the channel 4. Therefore, the terminal 2transmits CTS frames in the respective channels 6 and 7 and does nottransmit CTS frames in the channels 4 and 5. The base station normallyreceives the CTS frames in the channels 6 and 7 with the analog filter1202 covering the channels 4 to 7 and digital filters 1202 a, 1202 b,1202 c, and 1202 d for the respective channels 4 to 7. The base stationdetermines that the CTS frames are not received in the channels 4 and 5.The base station transmits one or a plurality of data frames or anaggregation frame in a band obtained by bundling the channels 6 and 7.The terminal returns BA frames in the channels 6 and 7 according towhether the data frames are normally received. The BA frames returned inthe channels 6 and 7 are frames having the same content. Note that theterminal may transmit one BA frame in the band obtained by bundling thechannels 6 and 7. Note that the base station extracts, in the digitalfilters 1201 a and 1201 b for the channels 1 and 2, signals of thechannels 1 and 2 from signals passed through the analog filter 1201.

As explained above, the terminal 2 extracts signals of the respectivechannels with the digital filters from signals passed through the analogfilter 1204. Actually, the terminal 2 applies

AGC (Automatic Gain Control) to the signals passed through the analogfilter 1204, processes the signals after the gain adjustment with thedigital filters, and extracts signals of the respective channels. Thesignals passed through the analog filter 1204 include an interferencesignal (a busy signal) in the channel 5. The amplitude of the signals isusually extremely larger than normally received desired signals of thechannels 4, 6, and 7. In the AGC, gain control is performed on the basisof total electric power. Therefore, the amplitude of the signals afterthe AGC are likely to be relatively extremely small compared with theamplitude of the busy signal. In this case, it is likely that signals ofnon-busy channels cannot be normally received (e.g., demodulated).

To suppress this problem, analog filters only have to be set for therespective channels in the terminal 2 and the base station as shown inFIGS. 16(A) and 16(B). Consequently, since the AGC is performedseparately for the respective channels, it is possible to prevent theproblem in which the reception in the other channels is affected by thebusy channel. In examples shown in FIGS. 16(A) and 16(B), in theterminal 2, analog filters 1408, 1409, 1410, and 1411 are respectivelyset for the channels 4, 5, 6, and 7. An analog filter 1407 is set in thechannel 1 in a period other than the MU-MC validity period. In the basestation, analog filters 1401, 1402, 1403, 1404, 1405, and 1406 arerespectively set in the channels 1, 2, 4, 5, 6, and 7 in the MU-MCvalidity period. Note that, in the base station, in a period other thanthe MU-MC validity period, basically, an analog filter may be set onlyin the channel 1 to perform the standby operation. The other channelsmay be turned off unless the other channels are used in particular.

FIG. 17 is a flowchart of an example of the operation of the terminalaccording to the first embodiment.

The terminal performs the standby operation in a system primary channel,which is a channel designated in advance (S101). When receiving a startnotification frame for notifying a start of the MU-MC communication, theterminal determines the own terminal is designated in the startnotification frame (S102). For example, the terminal performs thedetermination according to whether information for specifying the ownterminal (terminal specifying information) is included in the startnotification frame. As the information for specifying the own terminal,there is an AID or a MAC address of the own terminal, a group ID of agroup to which the own terminal belongs, or the like. As the startnotification frame, there is a beacon frame or a separately definedmanagement frame, or a control frame, or the like.

When the terminal specifying information of the own terminal is includedin the start notification frame, the terminal changes the standbyoperation channel to the channels for the MU-MC communication in timefor a start time of the MU-MC validity period (S103). The start time ofthe MU-MC validity period may be designated in the start notificationframe or may be designated in another frame beforehand. Alternatively,the start time of the MU-MC validity period may be decided in the systembeforehand as, for example, a time after fixed time from the receptionof the start notification frame. When a transmission time or a receptiontime of the start notification frame is the start time of the MU-MCvalidity period, the terminal only has to perform the channel changeimmediately after the reception of the start notification frame.

Note that, when the primary channel is not included in the channels forthe MU-MC communication, the standby operation may be performed in theprimary channel in addition to the channels for the MU-MC communication.As a method for changing the standby operation channels to the channelsfor the MU-MC communication, the change is sometimes performed bysetting of an analog filter, setting of digital filters, and setting ofboth of the analog filter and the digital filters. Examples of thesevariations are as explained with reference to FIGS. 12 to 16.

After receiving the start notification for the MU-MC communication, theterminal performs the MU-MC communication with the base station in thestandby operation channels (S104). For example, the terminal receivesRTS frames in the standby operation channels and returns CTS framesafter an SIFS in channels in which a carrier sensing result in fixedtime (a PIFS, etc.) before the reception is idle. The terminal stands byfor frames such as data frames in the channels in which the CTS framesare returned. When frames are normally received in the channels, theterminal returns ACK (or BA frames).

The terminal determines whether the MU-MC validity period has ended(S105). When the MU-MC validity period has ended, the terminal resetsthe standby operation channels to the original channel (the primarychannel, etc.) (S106). As a method of determining the end of the MU-MCvalidity period, an end time may be notified beforehand in a startnotification frame or a frame separate from the start notificationframe. When the own terminal is not designated as a target of the MU-MCcommunication in the next beacon frame, the terminal may determine thatthe MU-MC validity period has ended. Alternatively, when the startnotification frame designating the own terminal as the target of theMU-MC communication is not received by predetermined timing after thetransmission of the ACK frames within the present beacon interval, theterminal may determine that the MU-MC validity period has ended.

FIG. 18 is a flowchart of an example of the operation of the basestation according to this embodiment.

When determining a start of the MU-MC communication (S201), the basestation determines a terminal set as a target of the MU-MC communication(S202) and changes the standby operation channels of the own station tochannels used in the MU-MC communication (S203). However, the standbyoperation may be performed in the primary channel even if the primarychannel is not used in the MU-MC communication. The base stationgenerates a frame for notifying the start of the MU-MC communication (astart notification frame) and transmits the start notification frame inthe primary channel (S204). For example, information for specifying thedesignated terminal is included in the start notification frame.Besides, information for specifying channels used by the terminals inthe MU-MC communication, information for specifying a start time,information for specifying an end time, or a combination of these kindsof information may be included in the start notification frame. Theorder of step S202 and step S203 may be opposite.

After the transmission of the start notification frame, at the starttime of the MU-MC communication, which takes into account setup times ofthe terminals, or after the start time, the base station simultaneouslycommunicates with the terminals in the channels for the MU-MCcommunication (S205). For example, the base station transmits RTS framesto the terminals in the channels for the MU-MC communication for therespective terminals. The base station transmits frames such as dataframes or an aggregation frame after an SIFS in channels in which CTSframes are returned. The base station receives ACK frames of frames thatthe base station has successfully transmitted (or receives BA frames).If there are frames that the base station has failed in transmitting,the base station may retransmit the frames. Note that the base stationmay retransmit the frames in the following MU-MC communication or mayretransmit the frames in unicast communication after an end of thepresent MU-MC validity period.

The base station determines whether the MU-MC validity period has ended(S206). When the MU-MC validity period has ended, the base stationresets the standby operation channels to the original channel (theprimary channel) (S207).

In this embodiment, the end timing of the MU-MC validity period isdecided beforehand by, for example, designating the end time anddesignating the number of times of the beacon interval beforehand. Asanother method, a frame for notifying the end of the MU-MC validityperiod may be defined. The base station may end the MU-MC validityperiod by transmitting the frame. For example, an MU-MC Information 2field may be added, for example, behind or in front of the MU-MCInformation field of the frame format shown in FIG. 4. In the field, abit 1 may be set when the end is notified or a bit 0 may be setotherwise (or vice versa). Alternatively, it is also possible to notifythe end using a null bit of the HT control Middle subfield shown in FIG.6B. The terminal set as an end target only has to be designated by aninformation element of the format shown in FIG. 5(B). The informationelement only has to be set in a body field of a frame. The terminal thathas received the frame for notifying the end only has to reset thestandby operation channels to the original channel.

As explained above, according to this embodiment, by notifying the startof the MU-MC communication, the terminals perform the standby operationin the primary channel before the MU-MC communication startnotification. After the notification, the terminals switch the primarychannel to the channels for the MU-MC communication and perform thestandby operation in the channels for the MU-MC communication.Consequently, before the notification, it is unnecessary to perform thestandby operation in channels not in use. Therefore, it is possible toreduce power consumption. It is possible to further reduce the powerconsumption by performing the standby operation according to the starttime of the MU-MC validity period. Similarly, the base station performsthe standby operation in the primary channel before the determination orthe notification of the start of the MU-MC communication. After thedetermination or the notification, the base station switches the primarychannel to the channels for the MU-MC communication. Consequently,before the MU-MC communication, it is unnecessary to perform the standbyoperation in channels not in use.

Second Embodiment

In the first embodiment, the form in which the base station and theplurality of terminals communicate with each other is explained.However, the present invention can also be carried out when theterminals perform the MU-MC communication not via the base station. Forexample, one of the plurality of terminals is set on a transmission sideand two or more terminals among the remaining terminals are set on areception side to perform the MU-MC communication. Note that, as astandard for the terminals communicating with one another not via thebase station, WiFi Direct and the like are known. When a terminaladapted to the WiFi Direct enables a function of the terminal, theterminal is recognized as the base station from the other terminals. Itis possible to connect the terminals in a one-to-one relation or aone-to-multiple relation.

Third Embodiment

As described in the first and second embodiments, the channels withinthe predetermined frequency band are channel 1 to channel 8 and thesechannels are consecutive channels. Below, the consecutiveness will befurther described.

The channel numbers in the IEEE802.11 standard are provided at 5 MHzintervals, therefore, in the case of a channel width of 20 MHz, aninterval between channel numbers at which channels do not overlap is 4.In the present embodiment, consecutive channels in a channel set meanconsecutive channels that do not overlap. The channel numbers in theembodiment are for convenience, and ch.1 should be interpreted aschannel number 36 in the 5 GHz band in the IEEE802.11 standard and ch.2should be interpreted as channel number 40 in the 5 GHz band in theIEEE802.11 standard.

[5 GHz Band]

In the 5 GHz band of IEEE802.11 standard, since channel numbers arebasically used at 20 MHz intervals, there is no problem in using thechannels based on the actually used channel numbers.

[2.4 GHz Band]

On the other hand, in the 2.4 GHz band, as illustrated in FIG. 20,reference channel selection is performed at 25 MHz intervals (FIG.20(A)) in such as North America and China, and at 30 MHz intervals (FIG.20(B)) in Europe. Therefore, it may be performed at 25 MHz intervals(FIG. 20(A)) mirroring the selection for North America and China where,for example, ch.1 in the embodiment may be set to channel number 1 inthe 2.4 GHz band in IEEE802.11 standard and ch.2 may be set to channelnumber 6 in the 2.4 GHz band in IEEE802.11 standard. Alternatively, itmay be performed at 30 MHz intervals (FIG. 20(B)) mirroring theselection for Europe where, for example, ch.1 in the embodiment is setto channel number 1 in the 2.4 GHz band in the IEEE802.11 standard andch.2 is set to channel number 7 in the 2.4 GHz band in the IEEE802.11standard. Alternatively, as illustrated in FIG. 20(C), mirroring the 20MHz channel intervals in the 5 GHz band, ch.1 in the embodiment may beset to channel number 1 in the 2.4 GHz band in IEEE802.11 standard andch.2 may be set to channel number 5 in the 2.4 GHz band in IEEE802.11standard. FIG. 20(C) exemplifies a future possible channel selectionother than the ones in FIG. 20(A) and FIG. 20(B). However, in the caseof such as North America, China and Europe, when another wirelesscommunication system selects, as at least part of the channels, channelnumber 6 or 7 in the 2.4 GHz band, the frequency band partially overlapswith that of channel number 5. In this case, a frequency band in whichmutual wireless communication systems influence each other broadens, andchannel utilization efficiency decreases.

Fourth Embodiment

FIG. 21 shows an example of entire configuration of a terminal or a basestation. The example of configuration is just an example, and thepresent embodiment is not limited to this. The terminal or the basestation includes one or a plurality of antennas 1 to n (n is an integerequal to or greater than 1), a wireless LAN module 148, and a hostsystem 149. The wireless LAN module 148 corresponds to the wirelesscommunication apparatus according to the first embodiment. The wirelessLAN module 148 includes a host interface and is connected to the hostsystem 149 through the host interface. Other than the connection to thehost system 149 through the connection cable, the wireless LAN module148 may be directly connected to the host system 149. The wireless LANmodule 148 can be mounted on a substrate by soldering or the like andcan be connected to the host system 149 through wiring of the substrate.The host system 149 uses the wireless LAN module 148 and the antennas 1to n to communicate with external apparatuses according to an arbitrarycommunication protocol. The communication protocol may include theTCP/IP and a protocol of a layer higher than that. Alternatively, theTCP/IP may be mounted on the wireless LAN module 148, and the hostsystem 149 may execute only a protocol in a layer higher than that. Inthis case, the configuration of the host system 149 can be simplified.Examples of the present terminal include a mobile terminal, a TV, adigital camera, a wearable device, a tablet, a smartphone, a gamedevice, a network storage device, a monitor, a digital audio player, aWeb camera, a video camera, a projector, a navigation system, anexternal adaptor, an internal adaptor, a set top box, a gateway, aprinter server, a mobile access point, a router, an enterprise/serviceprovider access point, a portable device, a hand-held device, and so on.

FIG. 22 shows an example of hardware configuration of a wireless LANmodule. The configuration can also be applied when the wirelesscommunication apparatus is mounted on either one of the terminal that isa non-base station and the base station. Therefore, the configurationcan be applied as an example of specific configuration of the wirelesscommunication device shown in FIG. 2 or 3. At least one antenna 247 isincluded in the example of configuration; however, two or more antennasmay be included. When a plurality of antennas are included, a pluralityof sets of a transmission system (216 and 222 to 225), a receptionsystem (232 to 235), a PLL 242, a crystal oscillator (reference signalsource) 243, and a switch 245 may be arranged according to the antennas,and each set may be connected to a control circuit 212. One or both ofthe PLL 242 and the crystal oscillator 243 correspond to an oscillatoraccording to the present embodiment.

The wireless LAN module (wireless communication apparatus) includes abaseband IC (Integrated Circuit) 211, an RF (Radio Frequency) IC 221, abalun 225, the switch 245, and the antenna 247. The wirelesscommunication integrated circuit according to the present embodimentcorresponds, for example, to the baseband IC or a set of the baseband IDand RF IC. The wireless communication integrated circuit further includethe balun 225, switch 245, antenna 24 or a combination thereof.

The baseband IC 211 includes the baseband circuit (control circuit) 212,a memory 213, a host interface 214, a CPU 215, a DAC (Digital to AnalogConverter) 216, and an ADC (Analog to Digital Converter) 217.

The baseband IC 211 and the RF IC 221 may be formed on the samesubstrate. The baseband IC 211 and the RF IC 221 may be formed by onechip. Both or one of the DAC 216 and the ADC 217 may be arranged on theRF IC 221 or may be arranged on another IC. Both or one of the memory213 and the CPU 215 may be arranged on an IC other than the baseband IC.

The memory 213 stores data to be transferred to and from the hostsystem. The memory 213 also stores one or both of information to betransmitted to the terminal or the base station and informationtransmitted from the terminal or the base station. The memory 213 mayalso store a program necessary for the execution of the CPU 215 and maybe used as a work area for the CPU 215 to execute the program. Thememory 213 may be a volatile memory, such as an SRAM or a DRAM, or maybe a non-volatile memory, such as a NAND or an MRAM.

The host interface 214 is an interface for connection to the hostsystem. The interface can be anything, such as UART, SPI, SDIO, USB, orPCI Express.

The CPU 215 is a processor that executes a program to control thebaseband circuit 212. The baseband circuit 212 mainly executes a processof the MAC layer and a process of the physical layer. One or both of thebaseband circuit 212 and the

CPU 215 correspond to the communication control apparatus that controlscommunication, the controller that controls communication, orcontrolling circuitry that controls communication.

At least one of the baseband circuit 212 or the CPU 215 may include aclock generator that generates a clock and may manage internal time bythe clock generated by the clock generator.

For the process of the physical layer, the baseband circuit 212 performsaddition of the physical header, coding, encryption, modulation process,and the like of the frame to be transmitted and generates, for example,two types of digital baseband signals (hereinafter, “digital I signal”and “digital Q signal”). The baseband circuit 212, the CPU 215 or bothof them carries out processing regarding OFDMA. The baseband circuit212, the CPU 215 or both of them may control operations on atransmission filter and a reception filter according to a setting of aused channel(s) so as to extract signals of the channel(s). Anothercontroller which controls the filters may be provided and the basebandcircuit 212, the CPU 215 or both of them may output an instruction tothe controller to control the filters.

The filters to be controlled may be analog filters (in case of thefilters 222, 232) or digital filters.

The DAC 216 performs DA conversion of signals input from the basebandcircuit 212. More specifically, the DAC 216 converts the digital Isignal to an analog I signal and converts the digital Q signal to ananalog Q signal. Note that a single system signal may be transmittedwithout performing quadrature modulation. When a plurality of antennasare included, and single system or multi-system transmission signalsequivalent to the number of antennas are to be distributed andtransmitted, the number of provided DACs and the like may correspond tothe number of antennas.

The RF IC 221 is, for example, one or both of an RF analog IC and a highfrequency IC. The RF IC 221 includes a filter 222, a mixer 223, apreamplifier (PA) 224, the PLL (Phase

Locked Loop) 242, a low noise amplifier (LNA) 234, a balun 235, a mixer233, and a filter 232. Some of the elements may be arranged on thebaseband IC 211 or another IC. The filters 222 and 232 may be bandpassfilters or low pass filters.

The filter 222 extracts a signal of a desired band from each of theanalog I signal and the analog Q signal input from the DAC 216. The PLL242 uses an oscillation signal input from the crystal oscillator 243 andperforms one or both of division and multiplication of the oscillationsignal to thereby generate a signal at a certain frequency synchronizedwith the phase of the input signal. Note that the PLL 242 includes a VCO(Voltage Controlled Oscillator) and uses the VCO to perform feedbackcontrol based on the oscillation signal input from the crystaloscillator 243 to thereby obtain the signal at the certain frequency.The generated signal at the certain frequency is input to the mixer 223and the mixer 233. The PLL 242 is equivalent to an example of anoscillator that generates a signal at a certain frequency.

The mixer 223 uses the signal at the certain frequency supplied from thePLL 242 to up-convert the analog I signal and the analog Q signal passedthrough the filter 222 into a radio frequency. The preamplifier (PA)amplifies the analog I signal and the analog Q signal at the radiofrequency generated by the mixer 223, up to desired output power. Thebalun 225 is a converter for converting a balanced signal (differentialsignal) to an unbalanced signal (single-ended signal). Although thebalanced signal is handled by the RF IC 221, the unbalanced signal ishandled from the output of the RF IC 221 to the antenna 247. Therefore,the balun 225 performs the signal conversions.

The switch 245 is connected to the balun 225 on the transmission sideduring the transmission and is connected to the balun 234 or the RF IC221 on the reception side during the reception. The baseband IC 211 orthe RF IC 221 may control the switch 245. There may be another circuitthat controls the switch 245, and the circuit may control the switch245.

The analog I signal and the analog Q signal at the radio frequencyamplified by the preamplifier 224 are subjected to balanced-unbalancedconversion by the balun 225 and are then emitted as radio waves to thespace from the antenna 247.

The antenna 247 may be a chip antenna, may be an antenna formed bywiring on a printed circuit board, or may be an antenna formed by usinga linear conductive element.

The LNA 234 in the RF IC 221 amplifies a signal received from theantenna 247 through the switch 245 up to a level that allowsdemodulation, while maintaining the noise low. The balun 235 performsunbalanced-balanced conversion of the signal amplified by the low noiseamplifier (LNA) 234. The mixer 233 uses the signal at the certainfrequency input from the PLL 242 to down-convert, to a baseband, thereception signal converted to a balanced signal by the balun 235. Morespecifically, the mixer 233 includes a unit that generates carrier wavesshifted by a phase of 90 degrees based on the signal at the certainfrequency input from the PLL 242. The mixer 233 uses the carrier wavesshifted by a phase of 90 degrees to perform quadrature demodulation ofthe reception signal converted by the balun 235 and generates an I(In-phase) signal with the same phase as the reception signal and a Q(Quad-phase) signal with the phase delayed by 90 degrees. The filter 232extracts signals with desired frequency components from the I signal andthe Q signal. Gains of the I signal and the Q signal extracted by thefilter 232 are adjusted, and the I signal and the Q signal are outputfrom the RF IC 221.

The ADC 217 in the baseband IC 211 performs AD conversion of the inputsignal from the RF IC 221. More specifically, the ADC 217 converts the Isignal to a digital I signal and converts the Q signal to a digital Qsignal. Note that a single system signal may be received withoutperforming quadrature demodulation.

When a plurality of antennas are provided, the number of provided ADCsmay correspond to the number of antennas. Based on the digital I signaland the digital Q signal, the baseband circuit 212 executes a process ofthe physical layer and the like, such as demodulation process, errorcorrecting code process, and process of physical header, and obtains aframe. The baseband circuit 212 applies a process of the MAC layer tothe frame. Note that the baseband circuit 212 may be configured toexecute a process of TCP/IP when the TCP/IP is implemented.

Fifth Embodiment

FIG. 23(A) and FIG. 23(B) are perspective views of wireless terminalaccording to the fifth embodiment. The wireless terminal in FIG. 23(A)is a notebook PC 301 and the wireless communication device (or awireless device) in FIG. 23(B) is a mobile terminal 321. Each of themcorresponds to one form of a terminal (which may indicate a basestation). The notebook PC 301 and the mobile terminal 321 are equippedwith wireless communication devices 305 and 315, respectively. Thewireless communication device provided in a terminal (which may indicatea base station) which has been described above can be used as thewireless communication devices 305 and 315. A wireless terminal carryinga wireless communication device is not limited to notebook PCs andmobile terminals. For example, it can be installed in a TV, a digitalcamera, a wearable device, a tablet, a smart phone, a gaming device, anetwork storage device, a monitor, a digital audio player, a web camera,a video camera, a projector, a navigation system, an external adapter,an internal adapter, a set top box, a gateway, a printer server, amobile access point, a router, an enterprise/service provider accesspoint, a portable device, a handheld device, a vehicle and so on.

Moreover, a wireless communication device installed in a terminal (whichmay indicate a base station) can also be provided in a memory card. FIG.24 illustrates an example of a wireless communication device mounted ona memory card. A memory card 331 contains a wireless communicationdevice 355 and a body case 332. The memory card 331 uses the wirelesscommunication device 355 for wireless communication with externaldevices. Here, in FIG. 24, the description of other installed elements(for example, a memory, and so on) in the memory card 331 is omitted.

Sixth Embodiment

In the sixth embodiment, a bus, a processor unit and an externalinterface unit are provided in addition to the configuration of thewireless communication device according to any of the above embodiments.The processor unit and the external interface unit are connected with anexternal memory (a buffer) through the bus. A firmware operates theprocessor unit. Thus, by adopting a configuration in which the firmwareis included in the wireless communication device, the functions of thewireless communication device can be easily changed by rewriting thefirmware. The processing unit in which the firmware operates may be aprocessor that performs the process of the wireless communicationintegrated circuit, the first controller, the second controller or theplural processing of these elements according to the present embodiment,or may be another processor that performs a process relating toextending or altering the functions of the processing of the element(s).The processing unit in which the firmware operates may be included inthe bases station or the wireless terminal or both of them according tothe present embodiment. Alternatively, the processing unit may beincluded in the integrated circuit of the wireless communication deviceinstalled in the base station, or in the integrated circuit of thewireless communication device installed in the wireless terminal.

Seventh Embodiment

In the seventh embodiment, a clock generating unit is provided inaddition to the configuration of the wireless communication deviceaccording to any of any of the above embodiments. The clock generatingunit generates a clock and outputs the clock from an output terminal tothe exterior of the wireless communication device. Thus, by outputtingto the exterior the clock generated inside the wireless communicationdevice and operating the host by the clock output to the exterior, it ispossible to operate the host and the wireless communication device in asynchronized manner.

Eighth Embodiment

In the eighth embodiment, a power source unit, a power sourcecontrolling unit and a wireless power feeding unit are included inaddition to the configuration of the wireless communication deviceaccording to any of the above embodiments. The power supply controllingunit is connected to the power source unit and to the wireless powerfeeding unit, and performs control to select a power source to besupplied to the wireless communication device, Thus, by adopting aconfiguration in which the power source is included in the wirelesscommunication device, power consumption reduction operations thatcontrol the power source are possible.

Ninth Embodiment

In the ninth embodiment, a SIM card is added to the configuration of thewireless communication device according to any of the above embodiments.For example, the SIM card is connected with the MAC processor or thecontroller in the wireless communication device. Thus, by adopting aconfiguration in which the SIM card is included in the wirelesscommunication device, authentication processing can be easily performed.

Tenth Embodiment

In the tenth embodiment, a video image compressing/decompressing unit isadded to the configuration of the wireless communication deviceaccording to any of the above embodiments. The video imagecompressing/decompressing unit is connected to the bus. Thus, byadopting a configuration in which the video imagecompressing/decompressing unit is included in the wireless communicationdevice, transmitting a compressed video image and decompressing areceived compressed video image can be easily done.

Eleventh Embodiment

In the eleventh embodiment, an LED unit is added to the configuration ofthe wireless communication device according to any of the aboveembodiments. For example, the LED unit is connected to at least one ofthe MAC processor, the transmission processing circuit, the receptionprocessing circuit or the controller. Thus, by adopting a configurationin which the LED unit is included in the wireless communication device,notifying the operation state of the wireless communication device tothe user can be easily done.

Twelfth Embodiment

In the twelfth embodiment, a vibrator unit is included in addition tothe configuration of the wireless communication device according to anyof the first to fifth embodiments. For example, the vibrator unit isconnected to at least one of the MAC processor, the transmissionprocessing circuit, the reception processing circuit or the controller.Thus, by adopting a configuration in which the vibrator unit is includedin the wireless communication device, notifying the operation state ofthe wireless communication device to the user can be easily done.

Thirteenth Embodiment

In the thirteenth embodiment, the configuration of the wirelesscommunication device includes a display in addition to the configurationof the wireless communication device (which may indicate the wirelesscommunication device mounted in the terminal, the wireless communicationdevice mounted in the base station) according to any one of the aboveembodiments. The display may be connected to the first controller or thesecond controller in the wireless communication device via a bus (notshown). As seen from the above, the configuration including the displayto display the operation state of the wireless communication device onthe display allows the operation status of the wireless communicationdevice to be easily notified to a user.

Fourteenth Embodiment

In the present embodiment, [1] the frame type in the wirelesscommunication system, [2] a technique of disconnection between wirelesscommunication devices, [3] an access scheme of a wireless LAN system and[4] a frame interval of a wireless LAN are described.

[1] Frame Type in Communication System

Generally, as mentioned above, frames treated on a wireless accessprotocol in a wireless communication system are roughly divided intothree types of the data frame, the management frame and the controlframe. These types are normally shown in a header part which is commonlyprovided to frames. As a display method of the frame type, three typesmay be distinguished in one field or may be distinguished by acombination of two fields. In IEEE 802.11 standard, identification of aframe type is made based on two fields of Type and Subtype in the FrameControl field in the header part of the MAC frame. The Type field is onefor generally classifying frames into a data frame, a management frame,or a control frame and the Subtype field is one for identifying moredetailed type in each of the classified frame types such as a beaconframe belonging to the management frame.

The management frame is a frame used to manage a physical communicationlink with a different wireless communication device. For example, thereare a frame used to perform communication setting with the differentwireless communication device or a frame to release communication link(that is, to disconnect the connection), and a frame related to thepower save operation in the wireless communication device.

The data frame is a frame to transmit data generated in the wirelesscommunication device to the different wireless communication deviceafter a physical communication link with the different wirelesscommunication device is established. The data is generated in a higherlayer of the present embodiment and generated by, for example, a user'soperation.

The control frame is a frame used to perform control at the time oftransmission and reception (exchange) of the data frame with thedifferent wireless communication device. A response frame transmittedfor the acknowledgment in a case where the wireless communication devicereceives the data frame or the management frame, belongs to the controlframe. The response frame is, for example, an ACK frame or a BlockACKframe. The RTS frame and the CTS frame are also the control frame.

These three types of frames are subjected to processing based on thenecessity in the physical layer and then transmitted as physical packetsvia an antenna. In IEEE 802.11 standard (including the extended standardsuch as IEEE Std 802.11ac-2013), an association process is defined asone procedure for connection establishment. The association requestframe and the association response frame which are used in the procedureare a management frame. Since the association request frame and theassociation response frame is the management frame transmitted in aunicast scheme, the frames causes the wireless communication terminal inthe receiving side to transmit an ACK frame being a response frame. TheACK frame is a control frame as described in the above.

[2] Technique of Disconnection Between Wireless Communication Devices

For disconnection of the connection (release), there are an explicittechnique and an implicit technique. As the explicit technique, a frameto disconnect any one of the connected wireless communication devices istransmitted. This frame corresponds to Deauthentication frame defined inIEEE 802.11 standard and is classified into the management frame.Normally, it is determined that the connection is disconnected at thetiming of transmitting the frame to disconnect the connection in awireless communication device on the side to transmit the frame and atthe timing of receiving the frame to disconnect the connection in awireless communication device on the side to receive the frame.Afterward, it returns to the initial state in a communication phase, forexample, a state to search for a wireless communication device of thecommunicating partner. In a case that the wireless communication basestation disconnects with a wireless communication terminal, for example,the base station deletes information on the wireless communicationdevice from a connection management table if the base station holds theconnection management table for managing wireless communicationterminals which entries into the BSS of the base station-self. Forexample, in a case that the base station assigns an AID to each wirelesscommunication terminal which entries into the BSS at the time when thebase station permitted each wireless communication terminal to connectto the base station-self in the association process, the base stationdeletes the held information related to the AID of the wirelesscommunication terminal disconnected with the base station and mayrelease the AID to assign it to another wireless communication devicewhich newly entries into the BSS.

On the other hand, as the implicit technique, it is determined that theconnection state is disconnected in a case where frame transmission(transmission of a data frame and management frame or transmission of aresponse frame with respect to a frame transmitted by the subjectdevice) is not detected from a wireless communication device of theconnection partner which has established the connection for a certainperiod. Such a technique is provided because, in a state where it isdetermined that the connection is disconnected as mentioned above, astate is considered where the physical wireless link cannot be secured,for example, the communication distance to the wireless communicationdevice of the connection destination is separated and the radio signalscannot be received or decoded. That is, it is because the reception ofthe frame to disconnect the connection cannot be expected.

As a specific example to determine the disconnection of connection in animplicit method, a timer is used. For example, at the time oftransmitting a data frame that requests an acknowledgment responseframe, a first timer (for example, a retransmission timer for a dataframe) that limits the retransmission period of the frame is activated,and, if the acknowledgement response frame to the frame is not receiveduntil the expiration of the first timer (that is, until a desiredretransmission period passes), retransmission is performed. When theacknowledgment response frame to the frame is received, the first timeris stopped.

On the other hand, when the acknowledgment response frame is notreceived and the first timer expires, for example, a management frame toconfirm whether a wireless communication device of a connection partneris still present (in a communication range) (in other words, whether awireless link is secured) is transmitted, and, at the same time, asecond timer (for example, a retransmission timer for the managementframe) to limit the retransmission period of the frame is activated.Similarly to the first timer, even in the second timer, retransmissionis performed if an acknowledgment response frame to the frame is notreceived until the second timer expires, and it is determined that theconnection is disconnected when the second timer expires.

Alternatively, a third timer is activated when a frame is received froma wireless communication device of the connection partner, the thirdtimer is stopped every time the frame is newly received from thewireless communication device of the connection partner, and it isactivated from the initial value again. When the third timer expires,similarly to the above, a management frame to confirm whether thewireless communication device of the connection party is still present(in a communication range) (in other words, whether a wireless link issecured) is transmitted, and, at the same time, a second timer (forexample, a retransmission timer for the management frame) to limit theretransmission period of the frame is activated. Even in this case,retransmission is performed if an acknowledgment response frame to theframe is not received until the second timer expires, and it isdetermined that the connection is disconnected when the second timerexpires. The latter management frame to confirm whether the wirelesscommunication device of the connection partner is still present maydiffer from the management frame in the former case. Moreover, regardingthe timer to limit the retransmission of the management frame in thelatter case, although the same one as that in the former case is used asthe second timer, a different timer may be used.

[3] Access Scheme of Wireless LAN System

For example, there is a wireless LAN system with an assumption ofcommunication or competition with a plurality of wireless communicationdevices. CSMA/CA is set as the basis of an access scheme in IEEE802.11(including an extension standard or the like) wireless LAN. In a schemein which transmission by a certain wireless communication device isgrasped and transmission is performed after a fixed time from thetransmission end, simultaneous transmission is performed in theplurality of wireless communication devices that grasp the transmissionby the wireless communication device, and, as a result, radio signalscollide and frame transmission fails. By grasping the transmission bythe certain wireless communication device and waiting for a random timefrom the transmission end, transmission by the plurality of wirelesscommunication devices that grasp the transmission by the wirelesscommunication device stochastically disperses. Therefore, if the numberof wireless communication devices in which the earliest time in a randomtime is subtracted is one, frame transmission by the wirelesscommunication device succeeds and it is possible to prevent framecollision. Since the acquisition of the transmission right based on therandom value becomes impartial between the plurality of wirelesscommunication devices, it can say that a scheme adopting CarrierAvoidance is a suitable scheme to share a radio medium between theplurality of wireless communication devices.

[4] Frame Interval of Wireless LAN

The frame interval of IEEE802.11 wireless LAN is described. There aresix types of frame intervals used in IEEE802.11 wireless LAN, such asdistributed coordination function interframe space (DIFS), arbitrationinterframe space (AIFS), point coordination function interframe space(PIFS), short interframe space (SIFS), extended interframe space (EIFS)and reduced interframe space (RIFS).

The definition of the frame interval is defined as a continuous periodthat should confirm and open the carrier sensing idle beforetransmission in IEEE802.11 wireless LAN, and a strict period from aprevious frame is not discussed. Therefore, the definition is followedin the explanation of IEEE802.11 wireless LAN system. In IEEE802.11wireless LAN, a waiting time at the time of random access based onCSMA/CA is assumed to be the sum of a fixed time and a random time, andit can say that such a definition is made to clarify the fixed time.

DIFS and AIFS are frame intervals used when trying the frame exchangestart in a contention period that competes with other wirelesscommunication devices on the basis of CSMA/CA. DIFS is used in a casewhere priority according to the traffic type is not distinguished, AIFSis used in a case where priority by traffic identifier (TID) isprovided.

Since operation is similar between DIFS and AIFS, an explanation belowwill mainly use AIFS. In IEEE802.11 wireless LAN, access controlincluding the start of frame exchange in the MAC layer is performed. Inaddition, in a case where QoS (Quality of Service) is supported whendata is transferred from a higher layer, the traffic type is notifiedtogether with the data, and the data is classified for the priority atthe time of access on the basis of the traffic type. The class at thetime of this access is referred to as “access category (AC)”. Therefore,the value of AIFS is provided every access category.

PIFS denotes a frame interval to enable access which is morepreferential than other competing wireless communication devices, andthe period is shorter than the values of DIFS and AIFS. SIFS denotes aframe interval which can be used in a case where frame exchangecontinues in a burst manner at the time of transmission of a controlframe of a response system or after the access right is acquired once.EIFS denotes a frame interval caused when frame reception fails (whenthe received frame is determined to be error).

RIFS denotes a frame interval which can be used in a case where aplurality of frames are consecutively transmitted to the same wirelesscommunication device in a burst manner after the access right isacquired once, and a response frame from a wireless communication deviceof the transmission partner is not requested while RIFS is used.

Here, FIG. 25 illustrates one example of frame exchange in a competitiveperiod based on the random access in IEEE802.11 wireless LAN.

When a transmission request of a data frame (W_DATA1) is generated in acertain wireless communication device, a case is assumed where it isrecognized that a medium is busy (busy medium) as a result of carriersensing. In this case, AIFS of a fixed time is set from the time pointat which the carrier sensing becomes idle, and, when a random time(random backoff) is set afterward, data frame W_DATA1 is transmitted tothe communicating partner.

The random time is acquired by multiplying a slot time by a pseudorandominteger led from uniform distribution between contention windows (CW)given by integers from 0. Here, what multiplies CW by the slot time isreferred to as “CW time width”. The initial value of CW is given byCWmin, and the value of CW is increased up to CWmax everyretransmission. Similarly to AIFS, both CWmin and CWmax have valuesevery access category. In a wireless communication device oftransmission destination of W_DATA1, when reception of the data framesucceeds, a response frame (W_ACK1) is transmitted after SIFS from thereception end time point. If it is within a transmission burst timelimit when W_ACK1 is received, the wireless communication device thattransmits W_DATA1 can transmit the next frame (for example, W_DATA2)after SIFS.

Although AIFS, DIFS, PIFS and EIFS are functions between SIFS and theslot-time, SIFS and the slot time are defined every physical layer.Moreover, although parameters whose values being set according to eachaccess category, such as AIFS, CWmin and CWmax, can be set independentlyby a communication group (which is a basic service set (BSS) inIEEE802.11 wireless LAN), the default values are defined.

For example, in the definition of 802.11ac, with an assumption that SIFSis 16 μs and the slot time is 9 μs, and thereby PIFS is 25 μs, DIFS is34 μs, the default value of the frame interval of an access category ofBACKGROUND (AC_BK) in AIFS is 79 μs, the default value of the frameinterval of BEST EFFORT (AC_BE) is 43 μs, the default value of the frameinterval between VIDEO(AC_VI) and VOICE(AC_VO) is 34 μs, and the defaultvalues of CWmin and CWmax are 31 and 1023 in AC_BK and AC_BE, 15 and 31in AC_VI and 7 and 15 in AC_VO. Here, EIFS denotes the sum of SIFS,DIFS, and the time length of a response frame transmitted at the lowestmandatory physical rate. In the wireless communication device which caneffectively takes EIFS, it may estimate an occupation time length of aPHY packet conveying a response frame directed to a PHY packet due towhich the EIFS is caused and calculates a sum of SIFS, DIFS and theestimated time to take the EIFS. In the present embodiment, a wirelesscommunication system using parameters at such interframe spaces isassumed to be an interfering system with a wide communication range.

The terms used in each embodiment should be interpreted broadly. Forexample, the term “processor” may encompass a general purpose processor,a central processing unit (CPU), a microprocessor, a digital signalprocessor (DSP), a controller, a microcontroller, a state machine, andso on. According to circumstances, a “processor” may refer to anapplication specific integrated circuit (ASIC), a field programmablegate array (FPGA), and a programmable logic device (PLD), etc. The term“processor” may refer to a combination of processing devices such as aplurality of microprocessors, a combination of a DSP and amicroprocessor, or one or more microprocessors in conjunction with a DSPcore.

As another example, the term “memory” may encompass any electroniccomponent which can store electronic information. The “memory” may referto various types of media such as a random access memory (RAM), aread-only memory (ROM), a programmable read-only memory (PROM), anerasable programmable read only memory (EPROM), an electrically erasablePROM (EEPROM), a non-volatile random access memory (NVRAM), a flashmemory, and a magnetic or optical data storage, which are readable by aprocessor. It can be said that the memory electronically communicateswith a processor if the processor read and/or write information for thememory. The memory may be arranged within a processor and also in thiscase, it can be said that the memory electronically communication withthe processor.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions.

1. A wireless communication device comprising: a receiver configured toreceive a first frame notifying a start of resource unit-based OFDMA(Orthogonal Frequency Division Multiple Access) communication via afirst channel; and controlling circuitry configured to control, when thefirst frame is received, the receiver to perform standby operation atleast in a first resource unit in a second channel different from thefirst channel, wherein the first resource unit includes one or moresubcarriers among a plurality of subcarriers disposed in the secondchannel. 2.-20. (canceled)